Base on HSQLDB writing permission

Hello everyone,
I have connected Base to an existing HSQLDB. I managed to get this
connection working in so far as I can see the tables and contents but I
cannot add or modify data to/in the tables. I can create new tables but I
cannot add data to those newly created tables.

I checked user permissions and tried using an admin account to connect to
the database but the problem stays the same.

In a OO wiki (http://www.ooowiki.de/HsqlDb - sorry it's in german) I found
this information:
"After following the steps in this guide your data is available again.
Though gaining permission rights or copying a table into another database
does not always work."

"does not always work"???

Any help with this issue is appretiated.
Does OOBase not really support using a external HSQLDB?
What other external databses are then FULLY supported?
Is it a write permission issue?

Thanks,
Sebastian