The user receives the ORA 12560 error when starting SVRMGR or SQLPLUS.
To resolve this issue, perform these steps:
If the drive is Windows NT file system (NTFS), check the permissions on the drive or oracle home to be sure the system has full control on all sub-directories and files.
Be sure the instance is started. Go to Start > Settings > Control Panel > Services, and check if the database service is started.
Be sure the ORACLE_SID is set in the registry correctly. Go to Start > Run > type regedt32. Within the registry, select HKEY_LOCAL_MACHINE > SOFTWARE > ORACLE . Highlight ORACLE and select the left side ORACLE_SID = :.
To change ORACLE_SID, right click and select Modify. Enter the SID.This procedure is valid only when using DEFAULT_HOME. When you have another home, you need to highlight that home under ORACLE key, usually HOME1 HOMEx .
No spaces can be entered after the "=" when setting ORACLE_SID at the DOS prompt. Use Set oracle_sid=xyz, not set oracle_sid = xyz.
If you have verified that ORACLE_SID is properly set and the service is running, yet you still get an ORA 12560 error, it is possible that you have created an instance with a non-alphanumeric character. The Getting Started Guide for Oracle8i on Windows NT documents that SID names can contain only alphanumerics.
However, if you attempt to create a SID with an underscore or a dash on Oracle8i, you are not prevented from doing so. The service is created and started successfully, but attempts to connect fail with an ORA 12560. 6 error. In this scenario, the createdb scripts did not run correctly. An ORA 12560 using svrmgrl on WinNT is usually an indication that the OS system or environment is not set up correctly.