hi, Sithz
Thank you for posting your question here.
To answer your questions, first, I would think it is better to handle it on client side. Since you already know this is an error, why post back to server, and then send back to client and tell user, oops, sorry.
So, for your instance, I would recommend to use client script. Here is an example:
Code: JavaScript
function AJAXUploader1_OnClientError(control, error, message)
{
alert(control); //Here, you can do whatever you want.
//You can even use our Dialog control to show some fancy dialog.
alert(error);
alert(message);
}
Set ClientSideOnError="AJAXUploader1_OnClientError"
For detail, please see this link:http://www.essentialobjects.com/ViewDoc.aspx?t=JSDoc.Public.Global.uploader_error_handler.html
Thanks.