receiving Error: the system cannot find the path specified (write to disk)

[birch]

I started receiving this error message over a week ago. I made sure that I deleted all of the topics from the computer that I had viewed previously. That didn't help. I uninstalled bittorrent, reinstalled, same. I then installed utorrent, and that worked for about a week, now I am receiving the same error message. I can no longer download programs.