FinalSun doesn't always save tunnels properly, and as a result, your troops will get stuck in one of the corners. Make sure you test your tunnels extensively and fix all the errors, as it can be frustrating for players if they can't properly use the tunnels.
So after you've made your tunnel, open your map with notepad and go under the "tubes" section. There will be an extra -1 on some of them, where it should have the number before it instead. Change all of the -1's like the pic below:
![](http://lko.ppmsite.com/Public/Tibweb/MappingTutorials/fixingtunnelerrorrc6.png)
This tutorial is sponsored by tibweb.
Additional info by LKO:
-the lots of -1 are not necessary on each tube. It's enough to have only one -1 at the end.
-only max 127 tubes are possible (0-126). The tubes after 127th are ignored.
-each tunnel should be made with 3 adjacent tubes. Else the pathfinding has issues to get the unit through the tunnel automatically. (e.g. a 1x1 tunnel is rarely working)
-tunnels which start on one height level and end on another height level are not recommended. Units get stuck or leave the tunnel on a wrong height.