We updated telerik and facing some issues with that.
in new update with rich text editor has new property called MentionBox settings of that auto added in to designer code.
which creates an error when we run the application.
following line is auto added.
mentionBox1.FocusedItemIndex = -1;
we have to comment every time after doing UI changes. and we need to check every time whether that line is commented or not.
Please Help Us.