Unable to load *.gci files

[JohnAlexINL]

Literal text of the error dialog:

See the end of this message for details on invoking \njust-in-time (JIT) debugging instead of this dialog box.\n\n************** Exception Text **************\nSystem.ArgumentNullException: Value cannot be null.
Parameter name: source
  at System.Linq.Enumerable.ToList[TSource] (System.Collections.Generic.IEnumerable`1[T] source) [0x0000d] in <a38d71b964e545c18a1583170be4fc6f>:0 
  at ACSE.MainForm+<>c__DisplayClass92_0.<SetupEditor>b__0 () [0x0001c] in <63fb064f91884ecbb3709aaf3d824990>:0 
  at System.Threading.Tasks.Task.InnerInvoke () [0x0000f] in <94942505ad4c4982af4db0763017d52e>:0 
  at System.Threading.Tasks.Task.Execute () [0x00000] in <94942505ad4c4982af4db0763017d52e>:0 
--- End of stack trace from previous location where exception was thrown ---

  at ACSE.MainForm.SetupEditor (ACSE.Save save) [0x00460] in <63fb064f91884ecbb3709aaf3d824990>:0 
  at ACSE.MainForm.OpenSave (System.String saveFileLocation) [0x00097] in <63fb064f91884ecbb3709aaf3d824990>:0 
  at System.Runtime.CompilerServices.AsyncMethodBuilderCore+<>c.<ThrowAsync>b__7_0 (System.Object state) [0x00000] in <94942505ad4c4982af4db0763017d52e>:0 
  at (wrapper managed-to-native) System.Reflection.RuntimeMethodInfo.InternalInvoke(System.Reflection.RuntimeMethodInfo,object,object[],System.Exception&)
  at System.Reflection.RuntimeMethodInfo.Invoke (System.Object obj, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x0006a] in <94942505ad4c4982af4db0763017d52e>:0 

I'm using the latest version of Dolphin if that's relevant. I followed your guide on getting the *.gci from my save data, so I'm not sure what to do from here.

[Pushyves]

I'm unable to tell which operating system you're using from the error dialog, but ACSE is only built for Windows. So if you're on either Mac or Linux, you'll need a Windows wrapper for ACSE to work, as mentioned by the developer here.