since it happens on forms with file upload, it sounds like a server time out issue.
how big is the file you are attaching? can you try with a smaller file?
Your friends over here at WebAssist! These Dreamweaver extensions will assist you in building unlimited, custom websites.
These out-of-the-box solutions provide you proven, tested applications that can be up and running now. Build a store, a gallery, or a web-based email solution.