I just found a tough mission : installing and upgrading to v1.96 OFP after having installed ArmA II:OA on my PC. Actually OFP was first uninstalled to make some room for ArmA, however, I had to reinstall OFP again. Installing works fine to the point where you need to upgrade with the different patches.
I always get errors messages telling me that some MPmissions or resistance missions have errors :
File C:\Program Files\Codemasters\OperationFlashpoint\MPMISSIONS\1-12_D_FLAGFIGHT3.NOE.pbo: bad size: 150024 (old=150616, new=150024)
Edit : I solved this issue by copiing Resistance files from a PC where it works ... not too bad