Can't input OB

For actuators like Camera and others that use an input of an OB, when I put it in, it just dissapears. It never happens anywhere else where I input an OB. Why?

It dissapears if the OB that you have typed in doesn’t exist.

The capitallisation and spelling have to be the same

eg. if you have an object named Cube.009 , you can’t type cube.009 into the OB: spot. You would need to put Cube.009