I see that you are using server-side configuration and thus I suggest to set the AutoCloseDelay property on the server as follows:
ErrorNotification.Text = msg;
ErrorNotification.AutoCloseDelay = 0;
You could alternatively set it directly in the markup.
The property itself determines after what amount of milliseconds the notification will automatically close (the default is 3000 millisecond). If you set it to 0, the notification will not close automatically and you will control when this should happen.
You can directly test the property and the results when different values are set in our online demo below:
I hope that my reply is detailed enough and helpful, let me know how it goes.
the Telerik team
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