Check with your host about whether the 'upload_tmp_dir' temp directory is set, has space, and is writable. For the time being, FTP the XML product file into your /forum/includes/xml directory and try the XML link import instead, using the following in the text box:
Code:
./includes/xml/product_filename.xml
If you have an 'open_basedir' restriction in effect, see
this post.