[exim] user cannot delete own e-mails

Hello and cheers!
I'm running Exim4 on RHEL3 and suddenly (yesterday) a user claimed:
-she can read and send e-mails without problems
-she cannot delete anykind of received e-mails...
i checked out her e-mail folder ,but i cannot see something odd there;
all kind of folders have the similar uid and guid as for the other
users, which can do e-mailing without this problem...
What should cause this problem?
i'm trying to find similar problem by making google,but this special
user claims :i must fix it as soon as possible!
She states : she has never had this problem ,and she has used her
mailbox for 11 years.
She is using mozilla thunderbirsd as an e-mail client and as she tries
to delete anykind of e-mail ,she gets : internal server error!
I asked her to send me the right error code she is receiving ,but i
think got lost in this .
I will check out the problem at my work place ,but i wanted to share
firstly some expirience .
If someone knows about such kind of exim problem i'll be very glad if
you let me know!
Many thanks in advance!


krassen