Outlook 2007 IMAP problem

I have installed ESET Smart Security business edition on 3 pcs at work and am now having problems with Outlook IMAP account syncronization.

when Outlook attempts to syncronise the IMAP accounts I get the Outlook pop up error message "cannot establish connection to server, imap.1and1.co.uk is now in offline mode".

This doesn't happen all the time - just on say 1 in 5 syncronisations. But once the account is offline it stays offline.

I have tried contacting ESET tech support and they can't solve it. In conjunction with them we defaulted the firewall settings then set it up in interactive mode. We also reinstalled ESET. Each time it looks like the right ports are open on the firewall but the problem remains.

Any ideas?