Jawin-Calling a DLL Entry Point

All Jawin experts:

I am trying to write Java code to call the fucntion of native DLL.

Here is the signature of C function:

  void CALLING_CONVENTION mergepreviewfromxmlW (
 WCHAR* errorbuffer,
 int iChars,
 const WCHAR* datasetxml,
 const WCHAR*  outputfile=PDFOUTPUT_W);

the error buffer is passed to the function and iChars indicates the number
of characters the buffer can hold.  The dll writes the error string to the
buffer and I need to get the string back.By calling this function, a pdf
file should be generated.

I wrote the generic invoke code as follows:

byte[] response = myFuncPtr.invoke("AIGG::n4", 16, nbs, null,
ReturnFlags.CHECK_NONE);

The program is running without error, but no pdf file is generated.
Do I write the instruction string "AIGG::n4" correctly?

If I add the following code to figure out the error:

ByteArrayInputStream bais = new ByteArrayInputStream(response);
LittleEndianInputStream leis = new LittleEndianInputStream(bais);
String error = leis.readUnicodeString();
System.out.println(error);

the error was printed as 'NULL'.

I would appreciate it if any Jawin experts can help me to figure out the
right instruction string.

Thanks/Hua