I think this is the same thing I posted about a few weeks ago. There appears to be a flaw in Windows 7 that will not let you go back to the last page by using the back button.

The solution I was given was to go to control panel, find and fix problems, view all, then click on internet explorer performance and repair the problem. Unfortunately it only lasts a little while. This is apparently caused by some add on feature that interferres with the back button. The solution solves it temporarily. Another thing to try is to just shut down IE and then reopen it. That worked for me today.