Too focused about UnrealBuildTool.exe instead of researching the first error "invalid number of parameters" (which I should have) I only look at "UnrealBuildTool.Main: CompilationResultException: Error: OtherCompilationError" so now I know the return code 6 for UnrealBuildTool.exe means OtherCompilationError. I waste some more time and I go look at the code of UnrealBuildTool.exe in C:\UE\Engine\Source\Programs\UnrealBuildTool it’s C# and the entry point of the program is in UnrealBuildTool.cs I look for the word OtherCompilationError inside but it does not give me much info. I give up this lead.