The 4.1 release includes lots of new features some of which require the implementation of code that sometimes messes up with custom controls because the upgrade process migrates only the data, not custom controls and logic, which every user or developer can create. We will consider your suggestions regarding the error reports. If the issue is still at hand could you try and remove the control and then upgrade to our newer version?
the Telerik team
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system and vote to affect the priority of the items