diff --git a/config/vanilla/bootstrap.early.php b/config/vanilla/bootstrap.early.php
index 13924aa..278d498 100644
--- a/config/vanilla/bootstrap.early.php
+++ b/config/vanilla/bootstrap.early.php
@@ -56,4 +56,8 @@
             ->column('Archived', 'tinyint(1)', '0')
             ->set(false, false);
     }
+
+    // Delete the records with UserID=0 (Guests) from UserRole table
+    // FIX: https://github.com/topcoder-platform/forums/issues/108
+    Gdn::sql()->delete('UserRole',['UserID' => 0]);
 }
\ No newline at end of file
diff --git a/vanilla/applications/dashboard/models/class.usermodel.php b/vanilla/applications/dashboard/models/class.usermodel.php
index 78c1ddf..b2750d0 100644
--- a/vanilla/applications/dashboard/models/class.usermodel.php
+++ b/vanilla/applications/dashboard/models/class.usermodel.php
@@ -2493,6 +2493,10 @@ public function saveAdminUser($formPostValues) {
      * @param bool $RecordEvent
      */
     public function saveRoles($UserID, $RoleIDs, $RecordEvent) {
+        if(!$UserID) {
+            throw new Exception(t('UserID is invalid.'), 400);
+        }
+
         if (is_string($RoleIDs) && !is_numeric($RoleIDs)) {
             // The $RoleIDs are a comma delimited list of role names.
             $RoleNames = array_map('trim', explode(',', $RoleIDs));