I have this problem show up quite often. Usually around the time a user is required to change their password for domain access, and if they are in the habit of just letting the computer go into standby instead of shutting down at night. 99% of the time all that is required is a restart of the computer so that it trashes the old cached password. If that doesn’t work, try doing a “repair” of the connection to flush dns entries among others.
Let me know if this helps,