I found it very useful to register the dll. I have tested the sameple and made my dll in folder "C:\Program Files\Microsoft Visual Studio\Vfp98" so to register it I issued the following command
regsvr32 "C:\Program Files\Microsoft Visual Studio\Vfp98\comdata.DLL"
Then i got the message DllRegisterServer in regsvr32 C:\Program Files\Microsoft Visual Studio\Vfp98\comdata.DLL Succeded
Then it is working ok.