IE 5.x sending invalid data

[Christopher Kalos]

This is part of a series of error messages that we've received in the past
from IMP upon hitting "Send"

The result is always the same.  The message doesn't get sent, and in some
cases, the message won't go away.

Does anyone have any idea why it happens, other than just "IE is sending
invalid data?"  Any help would be appreciated, as seeing this error message
also means that IMP just wiped out the message body without sending anything
to the recipients.
=====
Warning: File Upload Error - No Mime boundary found after start of file
header in /home/httpd/html/horde/imp/compose.php3 on line 1
=====

Thanks,
CK