Impossible to reproduce. With Simutrans 120.0.1 r7395, pak128 2.5.2, Windows 7.
Looks like someone has gotten the same error: http://forum.simutrans.com/index.php?topic=14386.msg142656#msg142656
The error is vaguely familiar, but I can't find the discussion where we discussed, and possibly fixed, that error. Nor do I remember if it was about stadt_t or something else. It probably also only contained an image with the text, making it impossible for the forum search to index it.
Where/when did you get this error? Even if it is not re-creatable knowing roughly when you got it can help.
Found the other discussion: http://forum.simutrans.com/index.php?topic=14284.0
So this might be fixed already. Does this match what you were doing, gauthier?
Nope, I wasn't doing anything particular when it occured. Anyway I should update my simutrans.exe hehe !
Quote from: gauthier on June 23, 2015, 02:32:16 PM
Nope, I wasn't doing anything particular when it occured. Anyway I should update my simutrans.exe hehe !
Well, it probably happens when cities grow naturally and spontaneously on their own as well. But if it happened just as you were doing something else, it might have had something to do with that.
The nightlies should be pretty stable now, since there is little activity from developers so far this year.