Via samba, if a user is in 16 unix groups, and the user then attempts to go into 
a directory where they rely on the group permission letting them in, they get 
access is denied. A small snipit of truss output below:

stat64("proj/gc", 0xFFBFD890)                   = 0
send(16, "\0\0\0 dFF S M B 2\0\0\0".., 104, 0)  = 104
time()                                          = 1080646263
poll(0xFFBFE9A8, 3, 60000)                      = 1
read(16, "\0\0\0 f", 4)                         = 4
read(16, "FF S M B 2\0\0\0\01807C8".., 102)     = 102
stat64("proj/gc", 0xFFBFE078)                   = 0
stat64("proj/gc/*", 0xFFBFE078)                 Err#13 EACCES
stat64("proj/gc/*", 0xFFBFE078)                 Err#13 EACCES
open("proj/gc", O_RDONLY|O_NDELAY|O_LARGEFILE)  Err#13 EACCES

This user DOES have permission to go to this directory (can su to them, and then 
go in). By reducing the number of groups they are in to less than 16, they then 
get granted access.