If the report will not open in your browser a lot of time it could mean there is a corrupted cookie in your browser cache.
The first thing to try is clearing your browser cache and cookies. 99% of the time this clears up the issue.
In Internet Explorer you can go to Tools > Internet Options and then find the browser cache and cookies area to clear.
Here are some instructions for different browsers:
One thing to try is accessing the site from a different browser or computer to confirm the issue is tied to the browser.