If the problem is indeed a (some) long-line records, as Eric suggested,
then it may be possible to edit the LOG files to shorten the line into
several (in the interim, before a new release of listserv deals with it).
Long lines have become a prevalent structure in messages since the
onset of easily-uploaded word-processing documents that are saved without
the "Save as .... with Text with Line Breaks" being used. Lines (i.e.,
objects with a LF/CR or LF at the end) are actually a full paragraph long
in those cases. Long paragraph --> long line.
Peter