member not found for the method _Index in powerpoint

Hi
I am new to jawin and i have been trying to write a small powerpoint
application
However the code works well except the call for the _Index method in the
following code

DispatchPtr app = new DispatchPtr("PowerPoint.Application");

DispatchPtr preses = (DispatchPtr)app.get("Presentations");
Integer count = (Integer) preses.get("Count");

DispatchPtr pres =(DispatchPtr) preses.invoke("_Index",new Integer(1));

this method is used to get the first presentation opened in powerpoint.

the exception i am getting is the following
org.jawin.COMException: 80020003 : member not found

could you please help me out in this?

thanks a lot

Noel AOUN
Software Engineering student
ESIB -USJ -LEBANON

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