DS 6.9 SP6 on server 2012

I have DS 6.9 SP6 installed on several 2012 R2 servers and the console works just fine. On the first few I was able to set up DSWEB with no problem using .Net v4.5 Classic for the app pool.

On a few of them however, I cannot get dsweb to work. I just get a blank page when navigating to it. I've tried every IIS setting I can think of with no luck. The permissions are correct and I can navigate to the default web site, so I know IIS is working.

Upgrading to DS 7.1 or 7.5 is not an option.

Anyone else seen this?

Thanks.