The end of the shift in the 1L retreat section the mining crew just finished a right hand cut in #6 entry between 4 and 5 crosscuts. When attempting to advance the MRS's the MRS on the left was stuck. The CM was attached to the MRS with a wire rope. When attempting to pull the MRS the roof caved trapping the 3 machines. MSHA was notified and a K order was issued.