While I want to place the active rail on a modded planet (happens on multiple of them), i get the following error:

The mod Skek's Train Improvements (0.0.12) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event skeks-train-improvements::on_built_entity (ID 6)
skeks-train-improvements/active-rails.lua:500: attempt to index field '?' (a nil value)
stack traceback:
skeks-train-improvements/active-rails.lua:500: in function 'onActiveRailBuilt'
skeks-train-improvements/control.lua:47: in function <skeks-train-improvements/control.lua:46>

Additionally, if the active rail is placed by a construction robot, no combinator is placed on the active rail.

Thanks for the report, the new update should fix both issues, but lmk if it still has issues placing active rails on your specific planet. Also, bots will now place active rails with a combinator, but they still won't place rail combinators with the wires of the ghost. I'll try to fix that issue in the next update.

Awesome work, thanks for the quick fixes.