Hello I've been having this after updating to recent update i tried your method by disabling antivirus and run program as administrator but doesn't work.
The Sims 4 Studio - Version 3.1.5.7
System.AggregateException: One or more errors occurred. ---> System.ArgumentNullException: Value cannot be null.
Parameter name: path1
at System.IO.Path.Combine(String path1, String path2)
at S4Studio.Data.FileDb.Sims4FileTable.IncludeUnknownDLC(Game bg)
at S4Studio.Data.FileDb.Sims4FileTable.Init(Boolean load_simulation, Boolean is_reinit)
at S4Studio.Shared.AppModel.DoInit()
at System.Threading.Tasks.Task.InnerInvoke()
at System.Threading.Tasks.Task.Execute()
--- End of inner exception stack trace ---
---> (Inner Exception #0) System.ArgumentNullException: Value cannot be null.
Parameter name: path1
at System.IO.Path.Combine(String path1, String path2)
at S4Studio.Data.FileDb.Sims4FileTable.IncludeUnknownDLC(Game bg)
at S4Studio.Data.FileDb.Sims4FileTable.Init(Boolean load_simulation, Boolean is_reinit)
at S4Studio.Shared.AppModel.DoInit()
at System.Threading.Tasks.Task.InnerInvoke()
at System.Threading.Tasks.Task.Execute()<---