oerr ora 204
00204, 00000, "error in reading control file '%s' (block %s, # blocks %s)"
// *Cause: Disk read failure of control file
// *Action: Check if disk is online, if it is not, bring it online and try
// warm start again. If it is, then need to recover disk.
If you can access an UNIX server, you can retrieve the signification of oracle-based errors:
just log as dba (belonging to the dba group), and type: