Anybody ever seen this one?

Scheduler appears to  back up C drive ok, then just locks up sometime during
the backup of D:
dsmsched.log:
        02/25/2002 03:01:48 ANS1898I ***** Processed    73,000 files *****
        02/25/2002 03:01:51 ANS1898I ***** Processed    73,500 files *****
        02/25/2002 03:01:54 ANS1898I ***** Processed    74,000 files *****
        02/25/2002 03:01:58 ANS1898I ***** Processed    74,500 files *****
        02/25/2002 03:02:01 ANS1898I ***** Processed    75,000 files *****
        02/25/2002 03:02:05 ANS1898I ***** Processed    75,500 files *****
        02/25/2002 03:02:09 ANS1898I ***** Processed    76,000 files *****
         (nothing further)


Messages in dsmerror.log:

        02/25/2002 02:54:10 ANS1802E Incremental backup of '\\slbmpst4\c$'
finished with 11 failure
        02/25/2002 03:02:11 Mutex lock failed: 6.
        02/25/2002 03:02:11 Release mutex failed; reason 6.
        02/25/2002 03:02:12 Mutex lock failed: 6.
        02/25/2002 03:02:12 Release mutex failed; reason 6.
        02/25/2002 03:02:13 Mutex lock failed: 6.
        etc.
.
These "Mutex" errors continued for hours until the scheduler was stopped.

Any idea what causes this?  Hasn't recurred since the scheduler was
restarted.
This is WinNT 4.0, SP 6
Client is 4.2.0.0

Thanks.