Please, clarify better: are you getting the 25007 error ONLY for EHAM, or for all airports ? It might just be possible you simply forgot to reactivate EHAM, maybe because you thought there wasn't any need, since you haven't installed it anymore.
A scenery activation is NOT a file stored anywhere on your hard disk or in the FS9 folder, is stored in your Windows registry This is of course is much better because, you can remove Flight sim, reinstall it, remove the scenery, reinstall it, without any worries of losing your activation. This means, regardless if the scenery is installed or not, the activation for it is still there in you registry and, if you change hardware, it will ask if you want to reactivate.
So, you have two ways of getting rid of that message:
1) Activate the scenery: meaning be sure to reply YES to the question to reactivate. This will of course consume an activation.
2) If, for any reason, you don't want to use the scenery anymore on this machine, you can get rid of the activation question by removing your Serial Number in the registry. Open the registry with REGEDIT and look for this key:
There will be a "Serial Number" entry on the right, with your Serial Number. Remove the entry, and the question will not be made anymore.
I'm sorry if it seems a complex procedure but, the case were a user doesn't want to use a previously activated (and payed for) scenery anymore, just after an hardware upgrade, is not very common, and we are somewhat hesitant to put a "Clean Registry" button on the Addon Manager (or something like that), because too many people will hit that by mistake, losing their activation. For the same reason our Uninstaller removes *everything*, EXCEPT the Serial Number in the registry. Basically, we try to make it difficult to lose your activation by mistake.