Problem: Internet Explorer 8 won’t clear out authentication credentials and keeps signing you on to a site with a set of undesired creds. In this instance, you’ve likely told Internet Explorer to remember a user’s logon creds for a site with Windows authentication turned on. You want to log on to that same site with different user credentials, but you can’t get IE to bring back up the user logon dialog. Clearing out all browser data (Tools | Internet Options | Browsing History | Delete | check all boxes, clear Preserve favorite website data) doesn’t solve the issue.
Solution: Use Fiddler to delete the browser’s cookie header. Start Fiddler and use Tools | Automatic Breakpoints | Before Request. Open IE and navigate to the bothersome site. Click on the last entry in the sessions pane, then right click on the Authorization cookie in the right Headers pane and select Remove Header.
Flip back to IE and clear out all browser data again (Tools | Internet Options | Browsing History | Delete | check all boxes, clear Preserve favorite website data) .
Now switch back to Fiddler and click Run to Completion in the lower left pane.
At this point you should be presented with the familiar login dialog.