Win 2K DFS - Win95 PCs lose connection

We have a Win 2000 domain (native mode) with a domain
based DFS. All win 9x clients have DS Client loaded on
them. They can successfully access the DFS shares, BUT
after a user leaves the PC idle for a while (say 30 mins)
the user cannot access the DFS shares until he/she logs
off the PC and logs back in.

The message they get is "Access Denied". The win2k users
have no such problem, only the win95 users. I have DHCP
and WINS servers setup. And the clients use DHCP for WINS
resolution.