cannot set user id

["Neil R. Smith" <neils ariel met tamu edu>]

FC2, 2.6.10-1.771
NIS client with nsswitch.conf passwd entry 'compat nis'
/etc/passwd user entries of form '+username'

Problem:
Recently a user of our FC2 system found he wasn't able to ssh login
anymore. No other users (total <20) are experiencing this problem.

The ssh login fails with 'Connection to xxxxxxx closed by remote host.'
When root user su's to this account, say with 'su - username', error
is 'su: cannot set user id: Resource temporarily unavailable'

/var/log/messages records consecutive 'session opened' and 'session
closed' for the user, with same time stamp.
/var/log/secure records that sshd accepted the password for that user.
'ypwhich' reports correct NIS master.

To my knowledge there have been no system config changes across the
working/notworking time interval. 

Again, this user used to be able to login. All others except this user
can still login.

Any suggestions?
-Neil
-- 
Neil R. Smith, Comp. Sys. Mngr.         neils tamu edu
Dept. Atmospheric Sci., Texas A&M Univ. 979/845-6272 FAX:979/862-4466