>The app I have been helping on was vfp7, and worked fine on W7 and W10, but since upgrading the project to vfp9 the W10 just hangs - doesn't even load. The little blue circle just sits going round and round, and I eventually have to reboot. Nothing shows up in Task Manager either. I have run the Windows compatibility thing, and that said it changed a few things, but still no luck. It won't even run locally - if I put the whole thing on the W10 box, and try running it, I get the same results.
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>If anyone can shed any light...Thanks!

Do you have at least the VFP9 runtime (if not the full product) on the W10 machine? A runtime installer can be downloaded from http://www.foxpert.com/runtime.htm .

Does the app use any ActiveX or OLE controls that may require registration or separate installation?

Are there any hard-coded paths in the app or a config.fpw file, that are causing the app to look for files in folders that don't exist on that computer?

Can you try manually excluding your app and data files from real-time antivirus scanning?

You should not need to run VFP9 apps in Compatibility Mode on W10, but if you'd like to experiment you can use the method shown in the lower half of this link: http://www.laptopmag.com/articles/set-compatibility-mode-windows-10