Lots of Snip....
>
>I tried one example. But the error when DDEInitiate is 16.
>ie connection error. It asked me to open EXcel sheet or not, but it is not starting the DDE .

OK,
1) you have built the FP 2.6 app into an .exe
2) The .EXE must be 'findable'. Try placing the .EXE in the working directory or somewhere else in the DOS Path, or even better, try using RUN /N (from VFP) or SHELL() ( from VB) to run the exe before you try to connect.
3) Your DDEInitiate should use the name of the exe (without .exe) as the service name.
4) I'm not sure what the initial Topic should be, the example code should indicate this.