OpenCL can't be used from WCF service hosted in IIS

I developed a WCF (Windows Communication Foundation) service application and hosted it inside IIS. This application, through a c++\cli wrapper, calls a native c++ dll using OpenCL for some calculations. When I call the c++ library from a c# console application everything works fine. When I call the service from a client application it can’t find OpenCL (return -1001 in clGetPlatformIDs). I found that this is caused for the isolation levels of the application. My service, hosted in IIS, works in session 0, instead, to have accesso to the GPU, it should work in session 1. Is this the problem I’m encountering? Is there a way to turn on this feature for IIS? Or the service must be launched as a Windows Service with particular privileges? I have Windows 7 64 bit, and NVIDIA GTX260.
Tks to all.