It would be easier to help point out a mistake in your code if you actually supplied it.
From the error itself you can see that problematic is "Preview Queue Element" function, because it has a wrong type of input.
With lack of code i can only guess it's because you either supply wrong or invalid "queue" input.
EDIT:
By wrong or invalid i mean either wiring straight queue constant to the input without initializing the queue itself or possibly overwriting an exiting queue with a default value (or some other common mistake)
