The only files with a name including Interstellar and .dll on my computer are:
./.local/share/Steam/steamapps/common/Kerbal Space Program/GameData/WarpPlugin/Plugins/Interstellar.dll
./.local/share/Steam/steamapps/common/Kerbal Space Program/GameData/InterstellarFuelSwitch/Plugins/MiniAVC.dll
./.local/share/Steam/steamapps/common/Kerbal Space Program/GameData/InterstellarFuelSwitch/Plugins/InterstellarFuelSwitch.dll
I have taken a look at the KSP.Log file and found:
[ERR 11:36:40.958] ADDON BINDER: Cannot resolve assembly: Interstellar_Redist, Culture=neutral, PublicKeyToken=null
followed by lots of:
System.IO.FileNotFoundException: Could not load file or assembly 'Interstellar_Redist, Version=1.3.0.0, Culture=neutral, PublicKeyToken=null' or one of its dependencies.
File name: 'Interstellar_Redist, Version=1.3.0.0, Culture=neutral, PublicKeyToken=null'
So I think we might well be missing a file somewhere for this mod to properly operate...