What are you using for connect string in the GUI? Are you using just a "/" or a full TNS string like "sys/passwd@servicename"? If the latter is used, then you MUST have a static listener defined for the database in question. If not, then you will need a local connect in order to connect with the instance. If the DB is in a started nomount, you can also verify the settings by trying to connect to the DB using the same connect string that you set in the GUI. You may be getting an error from TNS about "blocking" connections. If this is the case, you can add the following directive to the tnsnames.ora file for this database:
(UR = A)
If that allows the connection the iDA will also be able to connect.
On windows you may need to enable NTS authentication in the sqlnet.ora file to allow a local (connect / as sysdba) connection to work.
Let us know if this helps.
Ernst F. Graeler
Product Specialist - Data Protection & Recovery BU