diff --git a/attendance.php b/attendance.php
index 3104624..8f6bdcd 100644
--- a/attendance.php
+++ b/attendance.php
@@ -54,7 +54,7 @@ if ($attforsession->rotateqrcode == 1) {
         // Check the token.
         if ($secrethash !== $_COOKIE[$cookiename]) {
             // Flag error.
-            print_error('qr_cookie_error', 'mod_attendance', $url);
+            throw new moodle_exception('qr_cookie_error', 'mod_attendance', $url);
         }
     } else {
         // Check password.
@@ -73,7 +73,7 @@ if ($attforsession->rotateqrcode == 1) {
             setcookie($cookiename, $secrethash, time() + (60 * 5), "/");
         } else {
             // Flag error.
-            print_error('qr_pass_wrong', 'mod_attendance', $url);
+            throw new moodle_exception('qr_pass_wrong', 'mod_attendance', $url);
         }
     }
 }
@@ -103,7 +103,7 @@ if ($attforsession->autoassignstatus && (empty($attforsession->studentpassword))
     $statusid = attendance_session_get_highest_status($att, $attforsession);
     $url = new moodle_url('/mod/attendance/view.php', array('id' => $cm->id));
     if (empty($statusid)) {
-        print_error('attendance_no_status', 'mod_attendance', $url);
+        throw new moodle_exception('attendance_no_status', 'mod_attendance', $url);
     }
     $take = new stdClass();
     $take->status = $statusid;
@@ -114,7 +114,7 @@ if ($attforsession->autoassignstatus && (empty($attforsession->studentpassword))
         // Redirect back to the view page.
         redirect($url, get_string('studentmarked', 'attendance'));
     } else {
-        print_error('attendance_already_submitted', 'mod_attendance', $url);
+        throw new moodle_exception('attendance_already_submitted', 'mod_attendance', $url);
     }
 }
 
@@ -136,7 +136,7 @@ if (!empty($qrpass) && !empty($attforsession->autoassignstatus)) {
     $fromform->status = attendance_session_get_highest_status($att, $attforsession);
     if (empty($fromform->status)) {
         $url = new moodle_url('/mod/attendance/view.php', array('id' => $cm->id));
-        print_error('attendance_no_status', 'mod_attendance', $url);
+        throw new moodle_exception('attendance_no_status', 'mod_attendance', $url);
     }
 
     if (!empty($fromform->status)) {
@@ -147,7 +147,7 @@ if (!empty($qrpass) && !empty($attforsession->autoassignstatus)) {
             // Redirect back to the view page.
             redirect($url, get_string('studentmarked', 'attendance'));
         } else {
-            print_error('attendance_already_submitted', 'mod_attendance', $url);
+            throw new moodle_exception('attendance_already_submitted', 'mod_attendance', $url);
         }
     }
 }
@@ -181,7 +181,7 @@ if ($mform->is_cancelled()) {
         $fromform->status = attendance_session_get_highest_status($att, $attforsession);
         if (empty($fromform->status)) {
             $url = new moodle_url('/mod/attendance/view.php', array('id' => $cm->id));
-            print_error('attendance_no_status', 'mod_attendance', $url);
+            throw new moodle_exception('attendance_no_status', 'mod_attendance', $url);
         }
     }
 
@@ -193,7 +193,7 @@ if ($mform->is_cancelled()) {
             // Redirect back to the view page.
             redirect($url, get_string('studentmarked', 'attendance'));
         } else {
-            print_error('attendance_already_submitted', 'mod_attendance', $url);
+            throw new moodle_exception('attendance_already_submitted', 'mod_attendance', $url);
         }
     }
 
diff --git a/classes/structure.php b/classes/structure.php
index c5d349f..839bd33 100644
--- a/classes/structure.php
+++ b/classes/structure.php
@@ -550,7 +550,7 @@ class mod_attendance_structure {
         global $DB;
 
         if (!$sess = $DB->get_record('attendance_sessions', array('id' => $sessionid) )) {
-            print_error('No such session in this course');
+            throw new moodle_exception('No such session in this course');
         }
 
         $sesstarttime = $formdata->sestime['starthour'] * HOURSECS + $formdata->sestime['startminute'] * MINSECS;
@@ -720,7 +720,7 @@ class mod_attendance_structure {
             if (substr($key, 0, 7) == 'remarks') {
                 $sid = substr($key, 7);
                 if (!(is_numeric($sid))) { // Sanity check on $sid.
-                    print_error('nonnumericid', 'attendance');
+                    throw new moodle_exception('nonnumericid', 'attendance');
                 }
                 $sesslog[$sid] = new stdClass();
                 $sesslog[$sid]->studentid = $sid; // We check is_numeric on this above.
diff --git a/db/upgrade.php b/db/upgrade.php
index 2ea545d..d3f1c16 100755
--- a/db/upgrade.php
+++ b/db/upgrade.php
@@ -650,6 +650,5 @@ function xmldb_attendance_upgrade($oldversion=0) {
         upgrade_mod_savepoint(true, 2021050700, 'attendance');
     }
 
-
     return $result;
 }
diff --git a/export.php b/export.php
index 24b7a7c..458dbc7 100644
--- a/export.php
+++ b/export.php
@@ -132,7 +132,7 @@ if ($formdata = $mform->get_data()) {
                 }
             }
         } else {
-            print_error('sessionsnotfound', 'attendance', $att->url_manage());
+            throw new moodle_exception('sessionsnotfound', 'mod_attendance', $att->url_manage());
         }
 
         $setnumber = -1;
@@ -207,7 +207,7 @@ if ($formdata = $mform->get_data()) {
         }
         exit;
     } else {
-        print_error('studentsnotfound', 'attendance', $att->url_manage());
+        throw new moodle_exception('studentsnotfound', 'mod_attendance', $att->url_manage());
     }
 }
 
diff --git a/messageselect.php b/messageselect.php
index 99d712a..d22075e 100644
--- a/messageselect.php
+++ b/messageselect.php
@@ -56,9 +56,8 @@ if (!empty($messagebody['text'])) {
     $messagebody = $messagebody['text'];
 }
 $PAGE->set_url($url);
-if (!$course = $DB->get_record('course', array('id' => $id))) {
-    print_error('invalidcourseid');
-}
+$course = $DB->get_record('course', array('id' => $id), '*', MUST_EXIST);
+
 require_login($course);
 $coursecontext = context_course::instance($id);   // Course context.
 $systemcontext = context_system::instance();   // SYSTEM context.
diff --git a/preferences.php b/preferences.php
index fe3e21a..12e0921 100644
--- a/preferences.php
+++ b/preferences.php
@@ -93,7 +93,7 @@ switch ($att->pageparams->action) {
         break;
     case mod_attendance_preferences_page_params::ACTION_DELETE:
         if (attendance_has_logs_for_status($att->pageparams->statusid)) {
-            print_error('cantdeletestatus', 'attendance', "attsettings.php?id=$id");
+            throw new moodle_exception('cantdeletestatus', 'attendance', "attsettings.php?id=$id");
         }
 
         $confirm    = optional_param('confirm', null, PARAM_INT);
diff --git a/renderables.php b/renderables.php
index 3a5b9ca..5bd7645 100644
--- a/renderables.php
+++ b/renderables.php
@@ -583,11 +583,11 @@ class attendance_user_data implements renderable {
                 $parts = explode('sess', substr($key, 7));
                 $stid = $parts[0];
                 if (!(is_numeric($stid))) { // Sanity check on $stid.
-                    print_error('nonnumericid', 'attendance');
+                    throw new moodle_exception('nonnumericid', 'attendance');
                 }
                 $sessid = $parts[1];
                 if (!(is_numeric($sessid))) { // Sanity check on $sessid.
-                    print_error('nonnumericid', 'attendance');
+                    throw new moodle_exception('nonnumericid', 'attendance');
                 }
                 $dbsession = $this->sessionslog[$sessid];
 
diff --git a/sessions.php b/sessions.php
index 091c7bb..a68c8ef 100644
--- a/sessions.php
+++ b/sessions.php
@@ -148,7 +148,7 @@ switch ($att->pageparams->action) {
         }
         $sessid = optional_param_array('sessid', '', PARAM_SEQUENCE);
         if (empty($sessid)) {
-            print_error('nosessionsselected', 'attendance', $att->url_manage());
+            throw new moodle_exception('nosessionsselected', 'mod_attendance', $att->url_manage());
         }
         $sessionsinfo = $att->get_sessions_info($sessid);
 
@@ -191,7 +191,7 @@ switch ($att->pageparams->action) {
         }
 
         if ($slist === '') {
-            print_error('nosessionsselected', 'attendance', $att->url_manage());
+            throw new moodle_exception('nosessionsselected', 'mod_attendance', $att->url_manage());
         }
 
         break;
diff --git a/warnings.php b/warnings.php
index bfb1ab8..a4f8bff 100644
--- a/warnings.php
+++ b/warnings.php
@@ -107,7 +107,7 @@ if ($data = $mform->get_data()) {
         $notify = $DB->get_record('attendance_warning', array('id' => $data->notid));
         if (!empty($id) && $data->idnumber != $att->id) {
             // Someone is trying to update a record for a different attendance.
-            print_error('invalidcoursemodule');
+            throw new moodle_exception('invalidcoursemodule');
         } else {
             $notify = new stdClass();
             $notify->id = $data->notid;