Everything looked ok (I could connect to the OWB Workspace, navigate through the project, open and deploy mappings, etc.), since I have tried to import new tables in the Oracle Schema.
As soon as I clicked on Import Database Object, I got the following (and cryptic) error:
Persistent Layer Error: SQL Exception
Class name: CacheMediator
Method Name: getSQLResult
Error Message from Persisten Layer: ORA-02085
If I clicked on OK, the next step was a grey window with much more known error Java null pointer exception.
I really needed to import the new tables I had created to be able to work, so I started Googling the error, with no success. After a considerable amount of time I got on this note:https://blogs.oracle.com/warehousebuilder/entry/advanced_properties_of_location_new_for_11gr2
"Note the property "User Global Name", it specifies the unique name of the database, which is composed of the database name and the domain, in the form of database_name.database_domain. If you see the error ORA-02085: database link *** connects to *** during the import of metadata of database objects into OWB. It may mean the database has the system parameter global_names set to true, but you did not select the option "Use Global Name" of the Oracle location, as a result, the generated database link name for the import doesn't include the global database name and hence cannot access the database."
Basically I needed to specify the DB global name in each location that specified a connection to the DB.
If you do not know the global name of your DB, this SQL query can give you a precious hand.
SELECT * FROM global_name;
So unregister your location, specify the DB global name option and register the location again.