>A table with a large fpt is copied (copy/xcopy,whatever). If I open (USE SHARED) that table during that copying, I get the error message 'Memo file is missing or invalid'. After the copying the error is gone. The table is perfectly okay.
>
>Is this a known quirck? Is this acceptable behavior?

It means that a program you use to copy a table files locks the .FPT file and VFP cannot open it. The same error could be caused by antivirus program as well when .FPT file is not excluded from real time scanning.