Disable it in the game video otpions settings then go to "C:\Users\User\Documents\My Games\RedOrchestra2\ROGame\Config\" open the file ROEngine.ini in a text editor and search for this entrie to verify to is completly disabled :
bDisablePhysXHardwareSupport=
There is 3 lines like this on this file, that must be set to =True, like this :
bDisablePhysXHardwareSupport=True