Sharepoint asks for authentication while processing a web service call

In sharepoint my web part is calling a web service. This web service does some heavey processing in the background. On large data sets the page asks for your username and password after a certin period开发者_StackOverflow中文版 of time before a response is returned. It seems to be timing out. What setting timing out and where do I change this limit?

http://support.microsoft.com/kb/912451 upping this value from 30 seconds has stop the autheication problem for me. Running into a new issue backend now for it timing out but the browser seems to be fine.