IF you have
not moved the entries for the newest scenery addons you activated in your FSX Scenery Library they should be at the top of the list, just go into the Library and
uncheck the boxes for everything you have added since the error started showing up. Let it rebuild your Scenery Cfg file, shut down FSX. Load and run FSX and the error should be gone. if it is then add each scenery one at a time by re-checking the box for the scenery in the Scenery Library. I would shutdown the sim after each added scenery and restart. When you get to the offending scenery you get the error again and now you have it pinpointed as to what to work with.
Uncheck that scenery again then
delete it from the Scenery Library using the delete area function of the Library.
Now you have to figure out where the path to that scenery area is wrong which is what the error message is telling you.