Why am I getting 405 errors after swappinng domain names?

I had oldsubdomain.xxx.com. Everything was working fine. Windows 2008 R2 IIS 7.5 running php sites. Also had SSL running and used for all sites.

So I needed to change to newsubdomain.xxx.com. Installed new cert and edited bindings... New subdomain is working. Kind of. When people try to login to our apps via SSO they are getting "405 - HTTP verb used to access this page is not allowed" after the SSO delivers their info.

Also oldsubdomain.xxx.com is now set up as an alias by our network team. It redirects to newsubdomain.xxx.com in your browser but gives the same "405 - HTTP verb used to access this page is not allowed". If you refresh the page is loads fine...

I checked the php handler and it is allowing all verbs. Where do I start troubleshooting this? As far as I know no other changes were made to the web server.

Module  DefaultDocumentModule
Notification    ExecuteRequestHandler
Handler StaticFile
Error Code  0x80070001

This may be the result of how your URL is formatted, I ran into a similar issue with a WordPress theme that had a preview function that didn't work on IIS 7.5.

The reasoning is explained here: http://forums.iis.net/post/1912220.aspx

Essentially, the issue was that the URL didn't have a trailing / at the end of the path which causes some conflicts with the default document when posting to it (more or less, the link above explains it better)

Example:

http://localhost/wp_site?preview=true&_wpnonce=a1ef3f4811

VS

http://localhost/wp_site/?preview=true&_wpnonce=a1ef3f4811

The second URL works perfectly whereas the first one throws up a 405 error