2nd Group Membership not being detected on a Share

[Dave]

  I have Sun Sol 2.5.1 with SAMBA 1.9.18p4. 
  It was compiled with the gcc compiler and these defines:
# This is for SUNOS5.4 and later (also known as Solaris 2.4 and later)
# contributed by Andrew.Tridgell at anu.edu.au
FLAGSM = -DSUNOS5 -DSHADOW_PWD -DNETGROUP \
         -DFAST_SHARE_MODES -DAUTOMOUNT -DQUOTAS
LIBSM = -lsocket -lnsl
AWK = nawk
  I use NIS to distribute usernames and group membership. 
  This machine is NOT an NIS Slave or an NIS Master, just a yp client.
  I have a group called "special" with 5 members. All of these users are in
different primary groups (none in special as a primary).
  I have a share defined:
[global]
  security = user
[network]
  comment = Network Storage
  path = /usr/local/network   <- chmod 1770 - Owned by root.special
  revalidate = yes
  force group = @special
  write list = @special
  valid users = @special
  create mode = 770
  directory mask = 770
;
  None of the 5 users can access this share. All 5 use Win95 computers
(None use NT with SP3). They are asked for a password, and the correct
password for that user results in an password error (as if it was wrong). 
  ***NOTE: If I comment out the revalidate = yes, then they can map the
drive. But... any directory that they create has their primary group
listed, not the special group.
  This tells me, somehow, SAMBA does not know how to use the information in
the yp group file. If I do a "ypcat group |grep special", I get an accruate
list of users for the special group.
  Any suggestions?
Dave