Web access custom controls in TFS 2015 RC

I've had a few custom web access controls in TFS 2013, which has been working perfectly well.
However, in TFS 2015 RC they do not work. During uploading process everything goes as expected, but in the WI forms TFS displays message, that control cannot be created. 
Is this a bug in RC version or web access controls creation proccess has been changed?
Thanks a lot