If you run VFP APP or EXE inside other VFP application with DO command it shares enviroment of the calling application and uses the same runtime regardless in which version called application is built. IOW, your VFP8 app will use VFP6 runtime and it could blow up if it uses any features not present in VFP6. If you want your VFP8 application use VFP8 runtime you've to run it as external EXE using VFP RUN command, SHELLEXECUTE() api, WSH Run method, e.t.c.

>I have an application written using VFP6. Recently, I have write an addon to the app using VFP8. I issue DO ("myapp.exe") to call my addon app.
>
>1. Will my addon app run using VFP6 runtime oR VFP8 runtime? Are they in seperate process?
>2. I also faced problem that, my VFP8 app will do something to any existing toolbar, and it may crash becoz some property not exist/difference valid value in VFP6 such as specialeffect.
>
>What is the "fact" of calling app with diff version?
>How to make them run "seperately"?