Error Message: Waitforconnectfailed

This proble seems to occur a lot over the last years, as I find a lot of complanes about it. The remotecomputer shows "Ready to connect" but i get this error. I tried restart the remotemachine (which is very unpleasent since it is located at a customers), restart my TV service, turn of IPv6 and flush my DNS.

Can you please FINALLY fix this Problem for good?