I've been giving my webhosts grief over this but is this their problem?
A completely fresh install of WP in a clean directory. FTP'd the WP files, created the db, WP set up the wp-config file, logged in. So far so good. Then the first thing I did was to go for Tools/Import to upload a WP backup from elsewhere. This loads the Importer but all I got was: Destination folder already exists followed by path to the Importer code.
Looking at the server with each of three FTP clients, I can see no folder there at all. It was a fresh new folder after all.
So I load the Importer manually from an unzipped file using one the FTP clients, and it works ok.
I've seen references in the forum to the structure of zip files being one possible cause (apart from the folder actually being there but invisible to the FTP program). But how does that play with WP supplied plugins? Remember this was the very first thing I did after installing WP.
Its going to make installing plugins like some WooThemes new stuff a bit tricky - they don't make all their new plugins available for download, only activating from within WP.