Those messages are NOT "weird" or unexpected, you are really confusing normal things, which your problem of not being able to add to the Scenery Library automatically, which is an entirely different thing.
The Esellerate Error -25001 SIMPLY means there IS a Serial Number for that scenery in the registry, but you typed it wrong. This is obviously fixed by selecting "Register Serial" from the Addon Manager and type the CORRECT Serial Number.
The Serial Number is NOT removed when Uninstalling, and it's NOT removed even when Uninstalling FS9, which obviously make sense (you wouldn't want to reinsert it every time you reinstall the scenery) so, none of this has anything to do with the installation, it's just you typed a wrong serial, the program is trying to activate it, and found it being wrong. The fix is very simple, see above.
The other message, which is requesting activation, is also normal, is not "weird", and it's simply indicates there IS a Serial Number for that product in the registry, but it hasn't been activated yet, probably because an hardware change. If you reply YES, it will obviously go online to check your Serial Number, and eventually report one of the two results: either the Serial was correct and you still had activations left, OR the Serial wasn't correct because you typed it wrong, in that case an error 25001 will appear, and you'll have to fix it, obviously by inserting the CORRECT Serial.
Again, nothing of this is strange, weird or unexpected, it's exactly what is supposed to happen but of course, if you insert wrong Serials, how ANY software could react to fix this ?
And, none of this is related to the fact your system has something wrong which apparently prevents you to add a scenery to the Scenery Library.
