I wonder why Foxpro - once in a while - is not detecting a very regular line "DO any.prg" when building an .APP

There is no macro replacement. It is a very direct DO. Like P_EVE
This separate PRG modify the content of some values like we do several other places in the whole program. They all works except one or two.
And just sometimes...not every time.

We can solve the problem by adding "External Procedure 'theprg'" and then the APP compiler will see it.
But why is this happenning?

This is quite ambarrassing. We have no means to know if all the .PRGs
are included in the APP, so it is either discovered by the client or when we make the demo in the runtime environment.

No error message, nothing is detected while the APP is built. We try the program here and it works just fine since the any.prg is in the directory... but when we install the customer with his data files and the .APP it generate an error message "File 'whatever' not found.

Anyone knows why???

I am wondering if this situation happens in other version (DOS or Visual) of Foxpro?

Thanks in advance