I have those messages quite often.
They appear when my network is overloaded and trains are starting to turn around at signals after the signalwaittime has expired.
If a train is waiting with his rearend partly in a PBS block which is already occupied by another waiting train then the first train can't reserve a path when ttrying to turn around, because it would intersect with the path of the other train.
The thing that is a bug about this, is that the train that can't reveres releases it's path so that another train is cabable to crash into the first train.
I already reported this bug.
Wie zich gelukkig voelt met het geluk van anderen, bezit een rijkdom zonder grenzen. (F.Daels)Still the best OS around