Error 1967 is (according to vfp8 help):

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Data environment is already unloaded (Error 1967)
The form is attempting to close tables as it shuts down.
AutoCloseTables is set to true (.T.).
Don't programmatically close the data environment tables.
The CloseTables method is being called before the form is closed.
Set AutoCloseTables to false (.F.).
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Basically it is saying that it is trying to close tables that are already closed.

Now I understand this is bad programming, but why is it an error ?
Why can't vfp just ignore this condition ? (maybe it is trying to teach us programming!).