PHP Framesets

I’ve been having this strange problem with a current web project I"m working on. I am using framesets and implementing .php pages for both frames. The basic framework is a splash page that leads to the index with the framesets. Testing locally and onto my server, the page works. However, when I upload it to the client’s host, after I click the splash page, the browser asks if I want to download the .php files from the framesets.

I’m assuming this is a hosting problem, but is there a common problem that I am unware that has to due with PHP and framesets?