Accessing POP account with Treo 755 isn't working

We have over two dozen Treo 755p phone issued. All users are accessing their
email via POP. We are using the included VersaMail and the users are fine
with the limitations.

I have one user who has had no issues accessing her mail for the last 1½
years. Suddenly, she can't access her GW via POP. I have given her a new
phone, and tried accessing it via my phone.

The Treo connects to the mail server, then appears to hang for 30 - 45
seconds. Then the "Checking for new messages" message flashes on the screen
and the phone reboots itself. Doesn't matter which phone I use, the same
thing happens, so it is related to her account. All other users are
connecting fine and I can access other accounts using her phone.

I can see the phone making the connection on the server. She has less than
20 messages in her GW. It works via IMAP, but with the VersaMail app, that
is significantly slower than POP. I have run an analyze/fix on her mailbox.
Any other ideas?