Need Help with HTTP Error 302

I'm having a problem with a website that keeps giving me an a HTTP error 302. I've searched the web and from what I've read says that the problem lies with the web site and not my transmission. According to the support people at the website, they have no problems but every time I try to upload a file that they wanted I keep getting the same 302 error. The data I've found on line is pretty technical and I'd like a simple answer to whether it's my fault or the web site's.

Can anyone enlighten me on why I might be getting this error.