When designers make changes to existing scenarios (especially when updating), it is just too easy to forget to unlock the area you wish to change because the designer lets you go in an make changes to an area AND seemingly save them even if the area is locked.

The designer should somehow warn players that the changes they are attempting to make will not register.  Either at save, or with each attempt.

For instance, at Save, a pop-up..

Some or all of the changes you have made have been rejected because their respective areas are locked.

+1, did that more than once, more than three times actually

This has got me a few times also - sometimes you think you unlocked the right thing, but you didn't -

Yeah, it would be great if it told you what exactly you needed to unlock, and had an option 'unlock these for me', but just a warning that you are being stupid is 90% of the way there.