Use of a 'struct' as an argument in DLL cal

Hi,
I'm new to JAWIN and trying it to call a DLL that talks to a Portable Media
Center Device.
The Export syntax of the DLL method looks like the following
long __cdecl MtpPlay(struct IWMDMDevice3 *)

From Java I now try to call this method in that DLL
...
      FuncPtr mtpPlay = new FuncPtr("MtpControl.dll", "MtpPlay");
      mtpPlay.invoke(0x0100, ReturnFlags.CHECK_HRESULT);
...

but I get the following error message back.
..
org.jawin.COMException: 8007007f: The specific procedure could not be found.
...

What could that be? That it is a 'struct' not an 'int' in the argument??

Thanks
Thomas