Error 91 when i only have a code line for open MATLAB from Visual Basic (VB) in Excel's Macros. What should I do?

This is the original code from the Example in MATLAB page, I put ' in all the lines but 2 (for create the variable and for open MATLAB). The error keeps appearing also with this 2 lines. What do I need to do?

Sub callMATLAB()

Dim MatLab As Object 'Dim Result As String

MatLab = CreateObject("Matlab.Desktop.Application")

'Calling MATLAB function from VB

'Assuming solve_bvp exists at specified location

'Result = MatLab.Execute("cd d:\matlab\work\bvp")

'Result = MatLab.Execute("solve_bvp")

'Executing other MATLAB commands

'Result = MatLab.Execute("surf(peaks)")

'Result = MatLab.Execute("a = [1 2 3 4; 5 6 7 8]")

'Result = MatLab.Execute("b = a + a ")

'Bring matrix b into VB program

'MatLab.GetFullMatrix("b", "base", MReal, MImag)

End Sub

TY ALL! ^_^