Yes, I had the same problem and its a real pain. The problem for me turned out to be my USB bus exceeding its max bandwidth. If you have USB messaging turned off, you may not even realise its going on. The device causing the USB to overload was my joystick/pedal combo setup (I have an old set of thrustmaster pedals and a saiteck stick that both connect through a rockfire USB converter) once I ditched the stick and pedals for a Logitech
extreme 3d pro, all the problems faded away and peeps started getting rescued.
Im not sure if I would have had the problem if I was not using USB keyboard and mouse, so other options I could have had were to use a non usb keyboard or put an additional usb controller card in my machine and run the stick and pedals through that.
Hope you get it fixed as SAR 4 is an awsome sim.