SQL Server Management Studio File Open dialog is very slow to change directories

I am running Microsoft SQL Server Management Studio    10.0.2531.0 on Windows 7 Professional.
I have an intermittent problem with the File Open dialog. Sometimes it works reasonably well, but often it takes a very long time (a few minutes) to change directory. While it is doing whatever it is doing, the dialog and all of SSMS becomes unresponsive - I can't even cancel the dialog. It sometimes changes the cursor to an hourglass and sometimes not.
I do not have this problem with any other application.
I can open File Open one time and have this delay for every single directory change or if I open the Look In dropdown then, after closing it I can open it again and it will work with normal delays.
It is slow more often than it is normal.
It makes accessing files very impractical.