I have a friend with a 7D2 that is getting a err01 message. Does anyone know anything about this? I think she was using the Tamron 150-600 lens but not sure. The salesperson at the local camera store said Canon would say it is Tamron's problem and that Tamron would say it is Canon's problem, that is why I think she was using the 150-600 but it could be another Tamron lense.
That's caused by an issue with the lens contacts -- could be either the lens or the body. Try cleaning the contacts on both pieces with a microfiber cloth moistened with rubbing alcohol. (I've heard vodka will work in a pinch.) Or it could be that the lens just isn't quite screwed on fully.
If that doesn't fix it, try different lenses to see where the problem is. Could be bad wiring to the contacts in either.