Hi Pete
Thanks for the quick reply, I kept investigating and think I've got it actually.
A while ago I used a few symbolic links/junctions to shift some orbx scenery from my main P3d directory to another SSD to save space, (Orbx stuff seems to insist on being in the p3d directory, at least if you use the Orbx scenery app).
I last ran makerunways before writing the symlinks and as I use my atc app, (proatc x) networked I only run makerunways directly from the exe every now and then.
The symbolic links should be transparent to the OS and do work fine for p3d but cause the error with makerunways. Once I deleted the links and copied the scenery files back to their "real" place all works fine, no error :)
So it was indeed a corruption of sorts, just a deliberate one on my part! (Note to self don't try to be clever just: (a) by a bigger SSD or (b) stop buying scenery!!)
Anyway as always thank you enormously for all your hard work on FSUIPC, Widefs and make runways. I use them all, what would the simming world do with you!
All the Best
Matt Attwell