Reports Prompting for Authorization
REPORTS: Browser Prompting for Authorization When Loading Reports
If you try to load a report in Reports Prompting for Authorization and get a Windows prompt to enter your user name and password then the server most likely has SQL Reporting Services installed on it. SQL Reporting Services uses the "/Reports" URL for its reporting interface. That happens to be the same URL Reports Prompting for Authorization uses for its reports.
You can change SQL's Reporting Services URL easily to avoid this conflict. Here is a web page that talks about how to do that.