we managed to make it working again somehow. Try to repat all steps in instructional video (don't forget to refresh GAC). Then PROBABLY helped server restart. Now we are back. At first attempt it didn't work then probably after that restart it is worknig.
Anyway it's not generally good situation. I'm Telerik's paying customer for long years. I tried almost first time to send official support ticket. I got reply after two days. They told me simply that Telerik Open Access is not part of my (expensive!) DevCraft Complete license. No advice, no help.
With all those changes with Telerik Data Access (no support, dropping designer from 2015.Q1, supporting only stupid code first approach...) I'm not sure to continue with TDA in future projects. It is or better it was best ORM but now I'm not sure.