Products won't download after purchase [SOLVED]

After the customer makes a purchase they sign into their account and go to the download section for their product. The products show up, but when you click on them they won't download. The page just refreshes. The products are PDF files.

I've tried different themes but the issue is the same. I don't know if it's an OpenCart instal problem or an issue with the server.

I'm using v1.5.3.1

Any help or direction is greatly appreciated.

Thank you.

I ended up solving the issue. I did it by backing everything up and upgrading to the newest version of opencart. There must of been some corrupt file somewhere.