If you load a P4 cone (for example) from the Prop Types pallet and zRotate it 90 degrees you will have gimbal lock, the x and y Rotate dials will have the same effect. One way to work round gimbal lock without editing the prop is to load another prop in the document, line its x, y, and z translations up with your gimbal locked prop (without changing any of its rotations), then parent the original prop to the new one. Now hide the new prop and use its yRotate dial to get your missing rotation back.