Remove the Oracle configuration file
UNIX Cell Manager
/etc/opt/omni/server/Integ/config/Oracle8
Windows 2003 Cell Manager
Program Files -> Omniback -> COnfig -> Server -> Integ -> Config -> Oracle8
Windows 2008 Cell Manager
ProgramData -> Omniback -> COnfig -> Server -> Integ -> Config -> Oracle8
The configuration file will be named [instancename]%server name without the [ ] marks
This will mean that you are starting off fresh, creating a new Configuration file