Email problem

[Linda]

I have a strange email problem and have not had any luck tracking down.
I currently have an imap server using dovecot with maildir. I use 
fetchmail and procmail to sort and deliver mail. Periodically we will 
have a totally blank email.  When I look in the procmail.log I have an 
error message

Couldn't create or rename temp file "home/username/Mail/new/msg.whatever"

If I go to var/mail/username the message is there and in the users 
/home/username/Mail/new directory I have a 0 byte file

I have had it happen one or two time in the last 5 months with most of 
my users, however I have one user who this happens to a few times a day. 
She also has her email setup so it syncs to her blackberry  Our email is 
handled by the ISP and we pick it up from them with fetchmail so she is 
alerted when the ISP gets the mail. Now her blackberry copy goes through 
fine and when she has the blank email she just forwards it from the 
blackberry and the forward goes through.


Does anyone have any ideas at what causes this or where I should look 
for a solution?  I've done a lot of searching but am not coming up with 
anything that makes sense.
               
             Thanks
               Lidna