Hi, under Windows 7 Service Pack 1 with Platform Update you cannot use any D3D_FEATURE_LEVEL_11_1 and DXGI 1.2/WDDM 1.2 features.
This mean you can only use a limited set of Direct3D 11.1 under Windows 7 Service Pack 1 with Platform Update.
You can read more about here: Platform Update for Windows 7 (Windows)
PS: by the way you GFX Card (AMD Radeon 5950 series) does not support D3D_FEATURE_LEVEL_11_1.