disconnected without quit

I upgraded from 3.1.4 to 4.5.5 over the weekend

Everything seems find except for this :confused:

One of my users, her Blackberry through Vodafone in the UK (using pop3) stopped picking up the emails, I can see the connection coming through in the mailbox.log and getting a message "disconnected without quit".

At first I thought I solved it be re-indexing her mailbox, it was a 1.8Gb mailbox, it worked for about 4 hours and stopped again.

I then deleted her mailbox completely and created a new one, again it worked for about half a day and stopped again.

My own blackberry through a different carrier O2 and using imap has no problems. The other difference is I use only the web client as my main client, but she uses Entourage on a mac as her main client.

Can any one help?

Thanks
Ron