Question: How do I fix this error?

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),
    HorizontalGlue(),
    Button("Quit", Shutdown(), background=pink)
  ],
  "Find the locations of the vertical and horizontal tangents to the parametric curve.",
  [ TextBox[question](width=40, height=2, editable=false, background=white)
  ],
   BoxColumn(border=true, halign=none,
    caption="Step 1: Find the vertical tangent line:",
      halign=none,
       "Find x'. ",
     
      [halign=none,
       "x'= ",
       TextField[TFxp](width=15, background=turquoise),
       HorizontalGlue(),
       Button("Hint", Evaluate(function = "Htxp"), background="Orange"),
       Button("Check", Evaluate(function = "Ckxp"), background=green),
       TextField[MRxp](width=6, editable=false, background=white),
       Button("Show", Evaluate(function = "Shxp"), background=yellow)
      ],
     
       "Solve for t where x' equals 0.",
     
      [halign=none,
       "t= ",
       TextField[TFtv](width=15, background=turquoise),
       HorizontalGlue(),
       Button("Hint", Evaluate(function = "Httv"), background="Orange"),
       Button("Check", Evaluate(function = "Cktv"), background=green),
       TextField[MRtv](width=6, editable=false, background=white),
       Button("Show", Evaluate(function = "Shtv"), background=yellow)
      ],
        "Find the point where the curve has a horizontal tangent.",
      [halign=none,
       "x= ",
       Textfield[TFxv](width=15, background=turquoise),
       "  y= ",
       TextField[TFyv](width=15, background=turquoise),
       HorizontalGlue(),
       Button("Hint", Evaluate(function = "Htxp"), background="Orange"),
       Button("Check", Evaluate(function = "Ckxp"), background=green),
       TextField[MRxp](width=6, editable=false, background=white),
       Button("Show", Evaluate(function = "Shxp"), background=yellow)
      ]
  ),
  [ inset=0, spacing=0,
    "Instructor: ",
    "Programmers: ",
    "Copyright: "
  ]
]
)
):