Asp.net - Anonymous Authentication In IIS Over Https Does Not Fire A Postback?

I recently decided to change from using Windows Authentication for my internal web applications to Forms Authentication. I've not used the latter very much and one site explained you have to enable both Forms and Anonymous for this to work. The idea is to verify user passwords against an active directory then grant them access accordingly. I had this working just fine locally and when publishing to IIS 7.5 it still worked. It was just a basic Visual Studio project that would redirect to our homepage.

The problems arose when I tried accessing this same project securely with https, I included the full domain and it would load the new login page but when I clicked login it would do nothing. Since then I've scoured the web and found numerous mentions of this and that and tried many of them to no avail.

It was only later I created a blank project with a single button and one line of the code on the page to see if a post back had fired. After publishing I only enabled Anonymous Authentication in IIS and browsing to this basic test app using http when you clicked the button, false on the page changed to true - indicating a post back. Yet with https it just remains false. I think this may be why the active directory login wasn't working as it too had Anonymous enabled.

I'm still pretty new at the secure side of things but with the details passing over I have to use a secure connection just for the login then it can redirect to the usual applications we use internally.