It appears that our LISTSERV-NT started spewing these errors yesterday,
not long after doing a network table rebuild ....

  Error occurred while processing file 1329461 from LISTSERV@[many hosts]:

    Error X'0028004B' writing X-SUPD CMSUT1.

  Error traceback follows
  -----------------------
  >>> Error X'0028004B' writing file C:\LISTSERV\MAIN\X-SUPD.CMSUT1 <<<
   -> Severity: Error
   -> Facility: LFxxx routines
   -> Abstract: Record length larger than 65535
   -> I/O mode: Block write

Rebooting LISTSERV and the entire server (with a CHKDSK /F) did not help.
There is plenty of disk space, and we've had no problems like this before
yesterday.  Any ideas?