ORA-00203: Using the Wrong Control Files ORA-00203 is a critical Oracle database error that occurs during the MOUNT or OPEN phase of database startup when the instance detects that the control files being referenced do not belong to the current database. Oracle stores the database ID (DBID) and database name inside the control file, and if these values don't match the running instance, the startup is immediately halted. This error requires prompt DBA intervention as the database cannot be opened until the correct control files are identified and applied. Top 3 Causes 1. Control Files from a Different Database When multiple Oracle databases share the same server, it's easy to accidentally reference another database's control file in the CONTROL_FILES parameter. Oracle validates the DBID embedded in the control file against the instance's own DBID, and any mismatch triggers ORA-00203.…