Will the real error please stand up?

[OldProf]

I'm at work on another shunting scenario for the Woodhead Line (better known to me as the "Ya-Can't-Get-There-From-Here" route) and kept being flummoxed by "missing marker" errors. These tend to be confusing because the supposedly absent markers are identified by their "real" names rather than their "given" names. Well, I knew that the markers being identified as missing were indeed present, so some serious head scratching was in order ... ... ... ... ...

Eureka! The actual error was that I had entered some wagon numbers incorrectly in pick-up and drop-off instructions! {Side-bar: the Timetable Editor usually eliminates the need to enter wagon numbers manually, but lately it often refuses to detect a wagon's number when it is clicked.} Once I managed to put in the correct numbers, the "missing marker" errors went away.

Of course, now an AI train refuses to make its scheduled drop-off, but I'm putting that problem off until tomorrow.

"Woe is us", as Pogo used to say.