Usually we get this error if Oracle Client dosen’t know which database to connect according to “TNS Alias” information.

To control to status firstly we should check the connection manually over SQLPLUS with the related Oracle user.

Then we have to check ORACLE_SID environment variable defination on the system.

If not defined then we have to create like below to test it ;

C:\set ORACLE_SID=<SID>

After the test result don’t forget to assign this variable as permanent.

If you still getting the same error then please check the “Active Oracle Service Name”

OracleService<SID>

If service name is wrong then we have to delete and recreate again with the following steps ;

1 – Delete the wrong SID instance service

C:\oradim -delete -sid <SID>

2 – Define new service with right SID information

C:\oradim -new -sid <Yeni SID> -intpwd <parola> -startmode AUTO -pfile <init.ora>

Example ;

C:\oradim -new -sid DEV -initpwd PASSWORD -startmode AUTO -pfile C:\oracle11gR2\product\initDEV.ora