The maximum number of groups an user can belong to (both in AIX 5.3 and 6.1) is 128.
Check the /usr/include/sys/limits.h for information:
#define NGROUPS_MAX 128 /* max number of supplementary group IDs
per process, >= 0 */
The maximum number of groups that can be created on the system is 2000.
/usr/include/grp.h:
#define MAXGRP 2000
As stated before sound like problems with NFS
If the owner group of a file/directry was not within the first 17 groups of a user.
the users would not be able to write into that directory.
I believe that should be fixed in NFSv4.
Mike
"Whenever I dwell for any length of time on my own shortcomings, they gradually begin to seem mild, harmless, rather engaging little things, not at all like the staring defects in other people's characters."