Initialy the C# signature in this article used a public static readonly int for cbSize so it could be initialized inline but the static field is then no longer where you expect it to be in memory so the call to SHAppBarMessage() fails. The field cannot be static.

static extern IntPtr SHAppBarMessage(uint dwMessage,

  Shared Function SHAppBarMessage(ByVal dwMessage As Integer, ByRef pData As APPBARDATA) As Integer

    Shared Function SHAppBarMessage(ByVal dwMessage As Integer, ByRef pData As APPBARDATA) As Integer

    Dim ret As Long = SHAppBarMessage(CType(ABMsg.ABM_NEW, Integer), abd)

    SHAppBarMessage(ABMsg.ABM_REMOVE, abd)

    SHAppBarMessage(CType(ABMsg.ABM_QUERYPOS, Integer), abd)

    SHAppBarMessage(CType(ABMsg.ABM_SETPOS, Integer), abd)

    lRet = SHAppBarMessage(ABMsg.ABM_SETAUTOHIDEBAR, abd)

        state = SHAppBarMessage(CType(ABMsg.ABM_GETSTATE, Integer), ABD)

        hWndAppBar = SHAppBarMessage(CType(ABMsg.ABM_GETAUTOHIDEBAR, Integer), ABD)

        tsize = SHAppBarMessage(CType(ABMsg.ABM_GETTASKBARPOS, Integer), ABD)