This solved my problem :
You should check this directory /wordpress/wp-content/themes/ on your FTP and compare it with the original directory in the zip file on your harddrive. In this directory you should find the following subdirectories : classic & default. I found one empty subdir that carried the same name i had given to my blog site. I never created that directory so i guess it was created somewhere during the install. If you delete this subdir your problem should be solved.
Cheers
