Problems with flush_digests

Anyone able to help with some problem-solving for flush_digests, or 
able to explain the options that can be used in flush_digest.  I 
cannot find any documentation that explains it.  :(

I am getting the errors

Subject:        	Cron <slist@lists2> /u1/slist/.bin/flush_digests 

/usr/sbin/sendmail: invalid option -- -


another day I get 

/usr/sbin/sendmail: invalid option -- 7


I am used to the occasional breakage of digests and seeing the names 
of the affected lists in the error line, however, this sort of error 
has me flummoxed.

Anyone got thoughts?

Regards, Andrew