I keep getting this error and have no idea how to fix it.

Error, (in Elements:-Maplet) `Elements:-ElementTable[typ]` does not evaluate to a module

This is my code for the section with the error. Any help would be greatly appreciated.

FindParamTan:=Maplet(onstartup = RunWindow(MAIN),
Window[MAIN](title="Computing Vertical and Horizontal Tangents to Parametric Curves",
[ [ halign=none,
    Button("New Curve", Evaluate(function = "ask"), background=magenta),