Hi Dima,
The "ORA-12154: TNS could not resolve service name" error has many causes.
Please read:
http://www.dba-oracle.com/t_ora_12154_tns_...ervice_name.htm*************************************************************************
>> But client have so many tnsnames.ora files. Do you know which one I should use ?
Use the one that's specified in your registry:
http://www.dba-oracle.com/t_windows_multip...try_entries.htm*************************************************************************
You need to start debugging it. Start by opening a DOS window and try a "ping" to the server name.
Then, try a fully-qualified connect string to SQL*Plus.
See my checklist here, and report back where you hang:
http://www.dba-oracle.com/t_troubleshootin...vity_errors.htm