diff -Naur moodle2/user/index.php moodle/user/index.php
--- moodle2/user/index.php	2018-02-17 02:32:37.864706770 +0530
+++ moodle/user/index.php	2018-02-17 02:32:59.780707595 +0530
@@ -162,7 +162,14 @@
 
 if ($isseparategroups and (!$currentgroup) ) {
     // The user is not in the group so show message and exit.
-    echo $OUTPUT->heading(get_string("notingroup"));
+    //echo $OUTPUT->heading(get_string("notingroup"));
+    
+    // Above line has been commented out beacause changing the $string['notingroup'] didn't bring any change (moodle.php).
+    // Also making a change in the variable was also not a good idea as the variable's text might be required in some other place.
+    // Hence I have outputed what was desired!
+
+    echo "<span style = 'font-size:28px'> Sorry, but you need to be part of the selected group to see the participants.</span>";
+
     echo $OUTPUT->footer();
     exit;
 }