DLL import on wingetstate- Arguments start is nothing

[giorget]

I'm using the interop dllimport to use the function Wingetstate inside my application.

i'm using this line code:

<DllImport("Autoitx3.dll")> _

Public Shared Function AU3_WinGetState(ByVal title As String, Optional ByVal text As String = "") As Long

End Function

When i try to call the function by using try -catch cycle , i receive an error

Argument 'start' is nothing.

COuld you help me regarding that??

Thanks for support