Some of the common Oracle error codes:

ORA-12500: TNS:listener failed to start a dedicated server process
ORA-12541: TNS:no listener
ORA-12514: TNS:listener does not currently know of service requested
ORA-12154: TNS:could not resolve service name
ORA-12535: TNS:operation timed out
ORA-01017: invalid username/password; logon denied

ORA-00001 EXP-00054 ORA-00257 ORA-00600 ORA-00904 ORA-01008 ORA-01017 ORA-01092 ORA-01401 ORA-01422 ORA-01427 ORA-01460 ORA-01652 ORA-01653 ORA-01654 ORA-01830 ORA-01841 ORA-01843 ORA-01858 ORA-01861 ORA-02291 ORA-03115 ORA-03135 ORA-03505 ORA-04068 ORA-12154 ORA-12170 ORA-12500 ORA-12504 ORA-12505 ORA-12514 ORA-12518 ORA-12520 ORA-12528 ORA-12535 ORA-12541 ORA-12545 ORA-12560 ORA-12705 ORA-17002 ORA-17003 ORA-17041 ORA-20001 ORA-27101 ORA-28009 ORA-28547 ORA-30036 FRM-40505 FRM-40508 FRM-40735

Latest Forum questions:

ORA-00907: Substr
ORA-00907: Substr
ORA-12560: I am trying to login in the SQL PLus scott/tiger it will give an error ORA-12560: TNS:protocol adapter error please help
ORA-17114: ORA-17114: could not use local transaction commit in a global ...
TNS-03505: TNS-03505