Why are you upgrading to an outdated, unsupported version of Oracle? At least consider 9.2.
The error makes me think you're on Windows. Is the Windows thread space initialized / is the Windows service started?
Sometimes you will get this error if the registry key for the pfile has extra quotes (two single quotes is a bad thing) or hidden characters. Under the hive for your Oracle Home (the one used to start database, not the one used by odma) check the value of ORA_<SID>_PFILE. I would delete the value and rekey it.
When you attempt to start the database make sure you are using the Oracle Home that owns the database, not the new 901 Oracle Home until you get to the appropriate step in the upgrade process. Otherwisee the registry keys won't be available to you.