>>When I've done it first time after installing VFP8 the project which I changed in VFP8 stopped working in VFP7 with weird error in regard to an ActiveX which I am using in this application. Is it due to having both VFP7/VFP8 on the same box or projects cannot be edited interchangeably ?
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>What's the weird error? Can you please specify?

I've already figured this out. ActiveX contained a template which was saved as a string among its properties . When I updated a form in VFP8 this string was cleared for some reason , but it is nothing to do with VFP8 as such.