Email attachments cause my browser to close

This just recently started...I use Yahoo email & Gmail. When I attempt to attach a document or documents to an outgoing email message, during the 'attaching' process, my browser closes and I am reverted back to desktop...I can't figure this out....I suspect it is a minor setting somewhere that was changed by a downloaded program or the likes, but I don't know which settings to examine. I have a cable broadband connection and use a Netgear Router, but I haven't changed any of the wireless settings in the router. Also, the computer is running WinXP SP2, AVG Free, Ad aware and Spybot....Any suggestions on how to remedy this?