Optix SDK 5.1.0 Error C2039 'float2' isn't a member of 'optix'

Hi,I’m having some trouble building the Optix samples project !

After building the solution with Cmake , when I try to compile with Visual studio I get this error :

error 1 error C2039: ‘float2’ : isn’t a member of ‘optix’ C:\ProgramData\NVIDIA Corporation\OptiX SDK 5.1.0\include\optixu\optixpp_namespace.h 399 1 optixHello

I am using Windows 7 with Visual Studio 2012 and Optix 5.1.0, CUDA v7.5, CMake 3.7.0-rc2. Any ideas of what could be causing this error?