readqf: cannot open Q4/dflAF86OP3029019

This Solaris 2.8 server has about 24 sendmail processes running using the
"-q" option for various domains. The probem is that often that in the spool
directory the qf* files sometimes do not have a corresponding df* file. So
the header file exists but the message body file is missing . The
/var/adm/messages file is having error messages like the above every second
or so.
Where on earth do I look for the cause of this. ??
George