Sorry, steam does not show me notifications when you write here.

This is sometimes due to workshop failing to download it. Your system probably keeps the script in two places at once:
1: ...\Steam\steamapps\common\GarrysMod\garrysmod\addons
2: ...\Steam\steamapps\workshop\content\4000\287012681

This may also happen due to bad configuration so delete:
1: ...\Steam\steamapps\common\GarrysMod\garrysmod\data\trackassembly

Empty content of:
1: ...\Steam\steamapps\common\GarrysMod\garrysmod\download
2: ...\Steam\steamapps\common\GarrysMod\garrysmod\downloads
3: ...\Steam\steamapps\common\GarrysMod\garrysmod\cache

Validate the game cache, run the game and type:

"menu_cleanupgmas"

Or try my TA tutorial just for such cases:
https://github.com/dvdvideo1234/TrackAssemblyTool/wiki/Handling-runtime-errors

Please delete the data

thx