Why are you using PI Web Services instead of PI Web API? What are you trying to achieve?
We have some old client application, and original server (Win2008R2) is broken, so we got new one (virtual Windows2012R2).
In PIWebServices Release notes I found only Windows Server 2012, but not with R2
I had to install some Windows server features, like asp.net 3.5 support and IIS 6.0 Compatibility support