Runtime error there is no build provider registered for the extension ‘.cshtml’

This solved the problem for me.

Change this in Web.config

<compilation debug="true" targetFramework="4.5.1" optimizeCompilations="true" />

to

<compilation debug="true" targetFramework="4.5.1" optimizeCompilations="false" />

ADDED: when after a few minutes I back web.config to old, the problem not repeated. strange things )