> Connection string is
> "jdbc:firebirdsql://127.0.0.1/E:\\Data\\data.gdb"
> and all works ONLY when an Internet connection is established!

Then most likely it has something to do with the rounting. When you
establish connection with Internet the routing table contains an entry for
localhost. Though it sounds very strange...

Try asking in the Firebird-Support group, better not mention that you are
using JayBird - I suspect that at that point people stop reading and
redirect to this list :)

Roman