Are you using the "manage attachments" function at the bottom of the page ? You have the option of getting them from your computer or a URL (another site). I have better luck by copying the file to my computer first. Brouse the location where the file is (for me its my desktop), open the file, and then upload it. Depending on your network connection speed it may take a little time to upload it to this site. The manage attachment function will tell you what format is supported. Once your uploaded file is listed on your reply post it will not appear until you "post it" and the screen refreshes.