I was able to find a workaround at the PHP manager‘s site.
Just make sure you have .NET 3.5 installed and modify the following registry:
HKLM/System/CCS/Services/W3SVC/Parameters/MajorVersion
The value is 10 (Ax0). Just change the value to 9 (or 8), then try to install it again.
To avoid future issues with other IIS stuff, change back to 10 (Ax0). It seems that PHP Manager validates the value converting it into string or something related.
Here is the issue from PHP Manager‘s website:
