Autorecover - Default File Location

I'm having trouble with PowerPoint 2007's autorecover feature. Right
now, the default file location is set to "r". That's right, "r".
Since this strikes me as a little inaccurate, I tried to change it to
"C:\Users\{user}\Documents", which I know to be a valid path since I
can browse to it in Explorer and copy/paste this path directly into
the PowerPoint field. However, when I hit the OK button, I get the
following error message:

"The server drafts location you entered for offline editing is not
valid or you do not have permission to access that location. Specify
a location on you local computer."

I even tried to enter "c:\", but got the same error. This is the only
user account on the computer and does have administrator privileges,
so something is going wrong. Can anybody help?

Thanks.