modparam("usrloc", "db_mode", 0)

I can make calls between two users that are currently using my openser installation.

If I set 
modparam("usrloc", "db_mode", 1)

or
modparam("usrloc", "db_mode", 2)

It does not work any more and I get 408 errors, although the entries are written to the location table in the database and openserctl ul show –brief does show the users.

Any ideas ?

Thanks