Closing Outlook Express causing Error 623

Hi experts!
Outlook Express applies to: Windows/Windows XP/Networking, Mail and Getting Online. I just transformed to Wi-Fi from BT Voyager 105 modem. After that I have tried to uninstall my modem driver but I was unable to do so. When I tried to close outlook express, I get the error 623: unable to find postbox for this message.
I have no problem by sending and receiving messages. I am using Windows XP operating system SP3 and OE 2000.
Please help me. Thanks.
