Thanks for the input. We know that newgrp only works for the first 16 groups which are output by the groups command (sans this one problem group). The GID is in fact over 60000, but we have working...
I have a handful of users who can't 'newgrp' to one specific group from Solaris 9 and 10 nodes and always get this prompt:
newgrp: Password:
We never get prompted by 20+ other groups and this group...