When large zip files with a lot of files inside is uploaded, the httphandler throws an System.OverflowException "Value was either too large or too small for an Int32." This only happens in HTML 5 File API mode.
The problem is fixed in version 2013.2.611: http://www.telerik.com/products/aspnet-ajax/whats-new/release-history/q2-2013-version-2013-2-611.aspx