So, this is pretty simple, but it took me a few minutes to figure out what went wrong, so I thought I'd throw it up here.
I installed RDSH on a server that was already running RDWEB Access (I needed a RDSH in redirection mode and this box was not doing much at the moment...).
After a reboot I tested the RDWeb Access page, and I got this:
Internet Explorer cannot display the webpage
I scratched my head and checked the certificate I had bound to 443, and presto chango, it was suddenly missing.
Re-applying it fixed my issue and the website came right up.
But something to watch out for if you ever instal RDSH after RD Web Access.