Fix your PInvoke declaration.
Private Declare Auto Function sysUpdateDriverForPlugAndPlayDevices Lib "newdev.dll" Alias "UpdateDriverForPlugAndPlayDevices" (ByVal hwndParent As IntPtr, ByVal HardwareId As String, ByVal FullInfPath As String, ByVal InstallFlags As Integer, <Out()> ByRef bRebootRequired As Boolean) As Boolean