Website & file attachments

I hope it's not just me, but I generally have a terrible time getting attachments to work when I am posting. Sometimes they attach fine but usually I go through the trouble of writing a post, attach my screen shots, and afterwards find out the attachments don't work. When I try to "inline" the file and preview my post is when I usually find out the attachment didn't work because I get the message "The selected file could not be copied, because no file by that name exists. Please check that you supplied the correct filename". At that point I try different very unique filenames but it won't work. If I try later, usually the attachment will work, and using one of the previously tried filenames.