"Package Project" failed

Packaging my project fails with the infamous RunUAT.bat error. I’ve tried the several tips found here (i.e building UE4 with Development etc).

The same error happens with the pre-built engine, and with the engine built from source.

For completeness, here is the log:

MainFrameActions: Packaging (Windows (64-bit)): UE4Editor-Cmd: Execution of commandlet took:  12.28 seconds
MainFrameActions: Packaging (Windows (64-bit)): CommandUtils.Run: Run: Took 19,2771383s to run UE4Editor-Cmd.exe, ExitCode=1
MainFrameActions: Packaging (Windows (64-bit)): Project.Cook: Cook failed. Deleting cooked data.
MainFrameActions: Packaging (Windows (64-bit)): BuildCommand.Execute: ERROR: BUILD FAILED
MainFrameActions: Packaging (Windows (64-bit)): Program.Main: ERROR: AutomationTool terminated with exception:
MainFrameActions: Packaging (Windows (64-bit)): Program.Main: ERROR: Exception in AutomationScripts.Automation: Cook failed.
MainFrameActions: Packaging (Windows (64-bit)): Stacktrace:    at Project.Cook(ProjectParams Params) in c:\Users\Arvid\UnrealEngine\Engine\Source\Programs\AutomationTool\Scripts\CookCommand.Automation.cs:line 239
MainFrameActions: Packaging (Windows (64-bit)):    at BuildCookRun.DoBuildCookRun(ProjectParams Params) in c:\Users\Arvid\UnrealEngine\Engine\Source\Programs\AutomationTool\Scripts\BuildCookRun.Automation.cs:line 210
MainFrameActions: Packaging (Windows (64-bit)):    at BuildCommand.Execute() in c:\Users\Arvid\UnrealEngine\Engine\Source\Programs\AutomationTool\AutomationUtils\BuildCommand.cs:line 35
MainFrameActions: Packaging (Windows (64-bit)):    at AutomationTool.Automation.Execute(List`1 CommandsToExecute, CaselessDictionary`1 Commands) in c:\Users\Arvid\UnrealEngine\Engine\Source\Programs\AutomationTool\AutomationUtils\Automation.cs:line 392
MainFrameActions: Packaging (Windows (64-bit)):    at AutomationTool.Automation.Process(String[] CommandLine) in c:\Users\Arvid\UnrealEngine\Engine\Source\Programs\AutomationTool\AutomationUtils\Automation.cs:line 366
MainFrameActions: Packaging (Windows (64-bit)):    at AutomationTool.Program.MainProc(Object Param) in c:\Users\Arvid\UnrealEngine\Engine\Source\Programs\AutomationTool\Program.cs:line 134
MainFrameActions: Packaging (Windows (64-bit)):    at AutomationTool.InternalUtils.RunSingleInstance(Action`1 Main, Object Param) in c:\Users\Arvid\UnrealEngine\Engine\Source\Programs\AutomationTool\AutomationUtils\Utils.cs:line 708
MainFrameActions: Packaging (Windows (64-bit)):    at AutomationTool.Program.Main() in c:\Users\Arvid\UnrealEngine\Engine\Source\Programs\AutomationTool\Program.cs:line 53InnerException in AutomationUtils.Automation: BUILD FAILED: Failed while running Cook for C:\Users\Arvid\Perforce\xena\Unreal4\Xena.uproject; see log C:\Users\Arvid\UnrealEngine\Engine\Programs\AutomationTool\Saved\Logs\Cook-2015.09.09-21.37.28.txt
MainFrameActions: Packaging (Windows (64-bit)): Stacktrace:    at AutomationTool.CommandUtils.RunCommandlet(String ProjectName, String UE4Exe, String Commandlet, String Parameters) in c:\Users\Arvid\UnrealEngine\Engine\Source\Programs\AutomationTool\AutomationUtils\CommandletUtils.cs:line 212
MainFrameActions: Packaging (Windows (64-bit)):    at Project.Cook(ProjectParams Params) in c:\Users\Arvid\UnrealEngine\Engine\Source\Programs\AutomationTool\Scripts\CookCommand.Automation.cs:line 24
MainFrameActions: Packaging (Windows (64-bit)): ProcessManager.KillAll: Trying to kill 0 spawned processes.
MainFrameActions: Packaging (Windows (64-bit)): Program.Main: AutomationTool exiting with ExitCode=Error_UnknownCookFailure
MainFrameActions: Packaging (Windows (64-bit)): Domain_ProcessExit
MainFrameActions: Packaging (Windows (64-bit)): AutomationToolLauncher exiting with ExitCode=25
MainFrameActions: Packaging (Windows (64-bit)): copying UAT log files...
MainFrameActions: Packaging (Windows (64-bit)): RunUAT.bat ERROR: AutomationTool was unable to run successfully.
MainFrameActions: Packaging (Windows (64-bit)): BUILD FAILED
PackagingResults:Error: Error Unknown Cook Failure

Edit: Found something out: There is another error in here:

MainFrameActions: Packaging (Windows (64-bit)): UE4Editor-Cmd: [2015.09.09-19.45.35:940][  0]LogInit:Display: LogProperty:Error: UStructProperty::Serialize Loading: Property 'StructProperty /Game/Blueprints/UI/GameUI.GameUI_C:ExecuteUbergraph_GameUI.K2Node_MakeStruct_ChatMessage'. Unknown structure.

Ok, found the issue. I was creating a struct, without all of the members. I created a bug report for this.