VC problem during agent install

My maintenance contract is still valid ;-)

I have the same problem:

I have upgraded from working BE 2012 to BE 15. Everything fell into place (so it seems for now) except the fact that I cannot upgrade agents on any server.

My servers are also on local network with all ports opened. I am runnig SEP, have tried to disable it on targeted machine, but it did not help. Apparently there is a problem on target server with VC installation, but I can't tell from log what the obstacle is.

I would appreciate some help.