Error 1034 problems

Firstly I have very little programming knowledge, but I am trying to make some characters move when some buttons are pressed but I keep getting the error message:
TypeError: Error #1034: Type Coercion failed: cannot convert “[object MovieClip]0” to flash.display.MovieClip.
at Characters/onEnterFrame()
I have no idea what that means and after looking around the internet for hours I have still have no idea what it means. Can someone please tell me what is means. Thank you for reading and Sorry if this is in the wrong place on the forums or someone has already answered this question ages ago.