cvs process hung when i try to checkout or export...

[Dantld]

We have cvs pserver on Linux RedHat 7.3
server run string in xinted configuration:
cvs -f --allow-root=/home/cvs/repository --allow-root=/home/cvs/internal
pserv
(we support two repositories)

We try to export with command:
cvs export -d lib -r bserver_v_1_1 MGD/COMMON/bserver/bserver/lib

and command may be successful or no successful, when command not successful
we have one zombie process on a linux machine (where cvspserver are ran)
and client command wait infinitely, it can be interrupt by the Ctrl+C and
all cvspserver processes are exited...

ps output:
100 S sergey   10990   799  0  75   0    -  1328 schedu 09:58 ?
00:00:00 cvs -f --allow-root=/home/cvs/repository
--allow-root=/home/cvs/internal pserver
044 Z sergey   10991 10990  0  76   0    -     0 do_exi 09:58 ?
00:00:00 [cvs <defunct>] 0

We use config option
LockDir=/var/lock/cvs

Has anybody who can describe why cvspserver processes sometimes hunging?
Any ideas will be apprected.
Thanks in advance