Floor of K-Line 18" passenger car is stuck, cannot get it to move

K4680-308060 is an 18" O scale extruded aluminum passenger car,  I have removed the four screws which hold the floor and vestibule/end pieces to the side and roof.  I have removed the end pieces and unplugged the overhead lighting.  I've slid the floor about an inch and a half before it jammed.  Now I cannot move it either way.  Any suggestions as to how to get it moving?  Thank you, John in Lansing, ILL