permissions removing a directory?

[G. Willoughby]

I want to remove a directory but i keep getting this error:

OSError: [Errno 13] Permission denied: <path>

heres the code:

[snip]

self.workingDirectory=self.directory.get()
self.thumbnailDirectory=os.path.join(self.workingDirectory, "thumbnails")
if os.path.isdir(self.thumbnailDirectory):
    os.rmdir(self.thumbnailDirectory)

[/snip]

any ideas???

ta,

G. Willoughby