OE messages with attachments stuck in outbox

[Hersh]

I am running XP with SP2 and OE6.
In the past week I have developed a new problem with my Outlook Express:
When I send emails with attachments over about 40 or 50Kb, I get an error
box but the error message field is blank; the message says
"Some errors occured while processing the reqauested tasks. Please review
the list of errors below for more details."
Nothing appears in the list below. The email message appears to stay in my
outbox; it asks me to send it when I close and open the program; each time I
say "yes" it loops back to the same error box; it is, in fact sending the
message, but multiple times.
I have uninstalled my virus protection (provided by my server, Shaw.ca,
installed last week). The problem persisted. I have now reinstalled the
virus protection with email scanning in and out. I created a new OE
identity and imported all my old files and addresses. I thought that fixed
the problem but it didn't. There are several user profiles on this
computer, and the problem does not seem to exist on the other profiles.
Can anyone help me with a solution to this problem?
With thanks,
Hersh