"could not accept SSPI security context"

Hi,

I've set up 8.3 to use SSPI for authentication (clients and server on
windows XP). I can successfully connect from clients using psql and another
db client using SSPI authentication. However when trying to connect with
Npgsql (2.0.11) as the same user, the following error occurs:

"could not accept SSPI security context"

The same type of connection succeeds when connecting locally from the db
server. The problem only affects connection attempts on client machines, and
(currently) only when connecting from a .Net application using Npgsql. However
the same error also showed up when connecting with psql initially. Now that
works, and I'm not sure what change made that error disappear.

Can anyone help me understand that error? What circumstances can lead to
this?

Thanks,
Reto