the indication of "Windows cannot verify the digital signature for the drivers required for this device..." seem to me more like an unsuccessful mlnx_ofed v5.22 installation.
try uninstall the driver using "Programs --> uninstall a program" , reboot the machine, and install WinOF v5.22 from scratch
Downgrading to WinOF v5.10 is a good idea, just to compare and to rule out ant authentication or installshield signature issue that may be related to your Windows 7 OS preliminary dependencies