It appears that our LISTSERV-NT started sending these errors a week ago.

Error occurred while processing file 75765538 from LISTSERV@[many hosts]:

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

Error traceback follows
-----------------------
>>> Error X'0028004B' writing file D:\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 never had problems like this. 

 Any ideas?