Doug,
There were a number of fx files created during my early attempts to install AFLT lighting in airports. I got confused around the issue of AFLT FSX and P3D lighting and was not choosing the P3D4 LOD compiler. A number of fx_AFLT_*.fx files ended up in my main Effects folder, but after I discovered my compilation mistake, all these files were deleted from the main Effects folder and in AFLT folders. I have had a number of fresh starts with AFLT and only the latest successful one remains active. The previous attempts were deleted before I made a fresh start. As far as I am aware, the only place where previous fx files exist is in the recycle bin.
Having searched extensively for fx files produced by the P3D4 LOD compiler without success, I can only conclude that they are either hidden, or the compiler produces a light effect which is non-fx in the bgl files it produces.
I have also been seeking help in the P3D Other Support Questions forum about this issue and the latest development from a number of tests is that there seems to be a problem with FS Dreamteam Add-on Manager, which also has a number of fx files in an Effects folder. We have just today determined that it's not the fx files which are a problem, but there seems to be something else in Add-on Manager which causes the error popup to appear. The involvement of Add-on Manager in this whole matter was discovered when I unticked its box in P3Dv4.5 Add-ons screen and found that the sim loaded without the error popup. I am waiting for P3D to tell me what to do next.
Perhaps you can throw some light on the latest developments (if you'll forgive the pun!)