Hi Dhilip,
I tested the above successfully. What might be happening is that you have both the Policy Server and Web Agent on the same server, but they are different versions(12.8PS & 12.52 WA perhaps). While this does work, it can cause errors like this one.
In Windows, the PATH variable will point to both the Policy Server and Web Agent DLLs, some of which are common and share the same names. However if the versions don't match, the run time errors can occur.
You might be able to change the order of references in the PATH, but most likely you will need to separate the components onto different servers.
Hope this helps!