With codeplex gone it can be a bit hard to find the real download for some things. I had to search an old server archive to find this.
Php manager 1.2 x64,
This is the original v1.2 64bit download from 2012.
I also found the older 1.1.1 download should you want that instead,
HTTP Error 404.
The requested resource is not found.
Things that can cause this:
Verify that it did not stop the IIS website,
Verify your bindings are correct,
Verify that a firewall was not set incorrectly.
If you are getting this error:
Could not load file or assembly 'System.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The system cannot find the file specified.
First check that you have Microsoft.Web.Extensions.dll and Microsoft.Web.Extensions.Design.dll in your bin folder. Also check that you are using the correct version of .net in IIS.
If non of these solutions work then verify that if application is in a folder other than root you make this folder an application in IIS. Right click folder "convert to application".