Because my COM dlls respond erroneous with the above mentioned error 0x80080005 and some other times by the RPC_S_SERVER_UNAVAILABLE/1722, for simplicity I tried the WROX example - RemoteServer/RemoteClient.
The result I had was the same!
Server and Client machines belong to the same domain and use the NT4 OS.
Any modifications via DCOMCNFG has no result!
Also, I tried to use the same user name/password or to create a local account same as the Client.
The respond always the same: SERVER_EXEC_FAILURE
Thank you in advance,