Please check your scenery library to ensure all your non-Orbx add-ons are above the FTX entries. Use FTX Central/Settings/Library Insertion Point instead of moving things around with the in-sim Scenery Library. The latter doesn't always "stick" where using FTX Central does.
Also, a bad SODE installation can cause issues. Please see this thread for specifics.
Since Trondheim isn't a Mega Airport product, I moved this to the non-Mega Airport forum so others can find the thread more easily.
I'm sorry this is taking so long, too. I understand having too many projects at once, and it sounds like this is something you cannot delegate. I'm sure that those who developed it are anxious to see it released after all their efforts. Do the best you can when you can. As crechie said, we'll keep coming back and checking.
I think something is going wrong on their end because I suddenly started to get the same error message. I was using PFPX all week continuously and this morning, then I had to leave for 5 hours. Once I got back to get back to flightsimming I noticed this error message.
I am unable to do anything once I press ok button.