I guess your forms use Private data session. Change lookup form to use Default data session and it'll see the tables in DE of the parent form.

>It seems that this table / cursor is only accessible from the 'origin' form (the one with the DE).
>When I change the form, without closing the first one, this table isn't accessible / visible any more; switching back makes it usable again.
>
>Strange thing, I never came across this issue before.
>
>>What prevents you from that?