Just wondering if anyone has seen this before.

A user has had a signature consiting of a single jpeg file of the copany
logo etc.. This file was create by the deign team on a Mac.
Signature has been working fine until yesterday when it started to come up
with the little red "x" instead.
Attempts to recreate the signature using the same jpeg result in the same
problem, but the image does display correctly if editing the signature using
"advanced edit" (Word).
Other jpeg files work fine.
We opened the problem file using Paint and resved it as a jpeg. It now works