Hi David,
I had the same problem in the past but i fixed mine by supplying checking what TNSMANES.ORA user SIDADM user is using
and that you are able to do an 'tnsping SID' to the database you want to connect
let me know if you dont come right
just for info you can also test the connecting using DB02
From here you can create, modify and delete as well.
Best Regards
Marius