We are aware of this issue(it is observed only in the 2012.3.1205 version of our controls) and it is already fixed (you could test our latest internal build). In case you don't want to upgrade right now again you can avoid the exception by removing the filters declaration from mark up and set it from the code behind. Here is an example how it should look like:
sender, EventArgs e)
var filter =
Hope this will explain the issue and be helpful.
the Telerik team
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