[Samba] AD group member troubles

[Franz Ferdinand]

Hidiho!

I have a win2k network with AD and some samba servers. About 1.5 months 
ago suddenly one user could not access any files on any samba server (no 
probs on the win2k servers). A few days ago a second user couldn't 
access anymore any files on any samba server. Both can access files only 
if  the user has access rights but if only a group (where the user is a 
member of) is granted access it does not work. :(
One server was running for more than one year without making troubles 
and now this.
I tested it with Samba 3.0 RC2, 3.0.8, 3.0.9, 3.0.10 - every time the 
same problem.
On a test server I took smb.conf and nsswitch.conf from chapter 9 of 
"HowTo By Example" (but the oldest machine was running for more than one 
year without troubles and the config is nearly identically).
I'm using "Debian Sarge 3.0", kernel 2.4.27 (also tested with 2.4.18, 
2.4.21), Samba 3.0.10, MIT-KRB5 1.3.6...
I have about 50 users and more than 125 groups. Every user is member of 
several groups and file access is managed by groups. It seems as if I 
have reached some sort of limit (too many users, too many groups, 
whatever) and now the two guys (funny: my boss and our main hardware 
developer) can't work anymore :(
If I use wbinfo and getent I see a lot of groups for both guys but well 
- it don't work :(

Any ideas?

Greetings

   Franz

PS: Sorry for my bad english