Indeed, there is an error coming up. Seems like that BIS hasn't tested this. The problem is that the code returns something like: WEST 1-1-B:1 whereas a unit / object should be named like unit1. This might be caused by the streaming technology used by the engine (also prevents the usage of the command object, that's why it has been disabled in ArmA).
The solution? Give the object a name and replace the WEST 1-1.. with the name. So if you've got a unit1, change it to:
_camera camPrepareTarget unit1
And don't forget to report this as a bug, because I think it is (might miss something, tried deleting the ' and ' / replaced them, but both didn't help).