If you use Internet Explorer 9, then you won't be able to select multiple plugins or themes at a time, and you won't be able to drag and drop files from your computer.
All other main browsers like Firefox, Chrome, Safari and Opera support this function. The upcoming Internet Explorer 10 will also support this function.
Also make sure that you have the proper "permissions" to upload plugins and themes. If you don't, you may need to upload plugins and themes via a free FTP program like Filezilla.
Article ID: 72
Category: 1-Minute WP Launcher