installing purchased themes

Hi, I have recently installed WP through fantastico and the site works apart from the fact that I cant upload a purchased theme in a zip format (that WP asks for). I can choose a theme from the stock but not one I have purchased elsewhere, when I do upload it, the page returns and comes up with “The uploaded file could not be moved to /home/harr4447/public_html/wp/wp-content/uploads/2010/11.” can anyone help?