try this, you created a camera called _cam but then referred to it as _camera it should be ok now
_camera = "camera" camcreate [0,0,0]
_camera cameraeffect ["internal", "Back"]
;=== car2
_camera camSetTarget [-68957.58,51518.96,-49871.42]
_camera camSetPos [4121.12,4961.45,24.18]
_camera camSetFOV 0.592
_camera camCommit 0
@camCommitted _camera
~5
playMusic "joc"
titlecut ["Joint Operations Command Presents..","BLACK IN",2]
~2
;=== car2
_camera camSetTarget [-68957.58,51518.96,-49871.42]
_camera camSetPos [4121.12,4961.45,24.18]
_camera camSetFOV 0.700
_camera camCommit 3
@camCommitted _camera
~5
;=== chopper1
_camera camSetTarget [4100.82,4974.82,0.00]
_camera camSetPos [4076.76,4974.89,0.74]
_camera camSetFOV 0.700
_camera camCommit 0
@camCommitted _camera
~5
;=== chopper5
_camera camSetTarget [4100.82,4974.82,0.00]
_camera camSetPos [4076.76,4974.89,0.74]
_camera camSetFOV 0.700
_camera camCommit 0
@camCommitted _camera
~5