UE4 Crashing When Saving Project

At this moment in time i am working on a open world game that is very large in scale which could come into the problem, but within the last couple of days every time i go and save the level it crashes after 78% complete, now it only crashes the world when i have added meshes though the foliage system, it doesn’t seem to crash if i edit setting or blueprints within this level. Here is the crash report, any help would be much appreciated.

MachineId:5C7E591646C1E45E75715F8943733168

Assertion failed: NewPosition >= 0 [File:D:\BuildFarm\buildmachine_++UE4+Release-4.11\Engine\Source\Runtime\Core\Private\Windows\WindowsPlatformFile.cpp] [Line: 452]

UE4Editor_Core!FDebug::AssertFailed() [d:\buildfarm\buildmachine_++ue4+release-4.11\engine\source\runtime\core\private\misc\outputdevice.cpp:430]
UE4Editor_Core!FFileHandleWindows::Seek() [d:\buildfarm\buildmachine_++ue4+release-4.11\engine\source\runtime\core\private\windows\windowsplatformfile.cpp:453]
UE4Editor_Core!FArchiveFileWriterGeneric::Seek() [d:\buildfarm\buildmachine_++ue4+release-4.11\engine\source\runtime\core\private\hal\filemanagergeneric.cpp:774]
UE4Editor_CoreUObject!UStruct::SerializeTaggedProperties() [d:\buildfarm\buildmachine_++ue4+release-4.11\engine\source\runtime\coreuobject\private\uobject\class.cpp:1418]
UE4Editor_CoreUObject!UScriptStruct::SerializeItem() [d:\buildfarm\buildmachine_++ue4+release-4.11\engine\source\runtime\coreuobject\private\uobject\class.cpp:2281]
UE4Editor_CoreUObject!FPropertyTag::SerializeTaggedProperty() [d:\buildfarm\buildmachine_++ue4+release-4.11\engine\source\runtime\coreuobject\public\uobject\propertytag.h:145]
UE4Editor_CoreUObject!UStruct::SerializeTaggedProperties() [d:\buildfarm\buildmachine_++ue4+release-4.11\engine\source\runtime\coreuobject\private\uobject\class.cpp:1409]
UE4Editor_CoreUObject!UObject::SerializeScriptProperties() [d:\buildfarm\buildmachine_++ue4+release-4.11\engine\source\runtime\coreuobject\private\uobject\obj.cpp:994]
UE4Editor_CoreUObject!UObject::Serialize() [d:\buildfarm\buildmachine_++ue4+release-4.11\engine\source\runtime\coreuobject\private\uobject\obj.cpp:933]
UE4Editor_Engine!UEdGraphNode::Serialize() [d:\buildfarm\buildmachine_++ue4+release-4.11\engine\source\runtime\engine\private\edgraph\edgraphnode.cpp:264]
UE4Editor_BlueprintGraph!UK2Node_EditablePinBase::Serialize() [d:\buildfarm\buildmachine_++ue4+release-4.11\engine\source\editor\blueprintgraph\private\k2node_editablepinbase.cpp:175]
UE4Editor_BlueprintGraph!UK2Node_Event::Serialize() [d:\buildfarm\buildmachine_++ue4+release-4.11\engine\source\editor\blueprintgraph\private\k2node_event.cpp:46]
UE4Editor_CoreUObject!UPackage::Save() [d:\buildfarm\buildmachine_++ue4+release-4.11\engine\source\runtime\coreuobject\private\uobject\savepackage.cpp:4495]
UE4Editor_UnrealEd!UEditorEngine::Save() [d:\buildfarm\buildmachine_++ue4+release-4.11\engine\source\editor\unrealed\private\editorengine.cpp:3890]
UE4Editor_UnrealEd!UEditorEngine::SavePackage() [d:\buildfarm\buildmachine_++ue4+release-4.11\engine\source\editor\unrealed\private\editorengine.cpp:3947]
UE4Editor_UnrealEd!UEditorEngine::Exec_Obj() [d:\buildfarm\buildmachine_++ue4+release-4.11\engine\source\editor\unrealed\private\editorserver.cpp:4409]
UE4Editor_UnrealEd!UEditorEngine::Exec() [d:\buildfarm\buildmachine_++ue4+release-4.11\engine\source\editor\unrealed\private\editorserver.cpp:5494]
UE4Editor_UnrealEd!UUnrealEdEngine::Exec() [d:\buildfarm\buildmachine_++ue4+release-4.11\engine\source\editor\unrealed\private\unrealedsrv.cpp:744]
UE4Editor_UnrealEd!SaveWorld() [d:\buildfarm\buildmachine_++ue4+release-4.11\engine\source\editor\unrealed\private\filehelpers.cpp:531]
UE4Editor_UnrealEd!FEditorFileUtils::SaveMap() [d:\buildfarm\buildmachine_++ue4+release-4.11\engine\source\editor\unrealed\private\filehelpers.cpp:2153]
UE4Editor_UnrealEd!InternalSavePackage() [d:\buildfarm\buildmachine_++ue4+release-4.11\engine\source\editor\unrealed\private\filehelpers.cpp:2546]
UE4Editor_UnrealEd!FEditorFileUtils::PromptForCheckoutAndSave() [d:\buildfarm\buildmachine_++ue4+release-4.11\engine\source\editor\unrealed\private\filehelpers.cpp:3076]
UE4Editor_UnrealEd!InternalSavePackages() [d:\buildfarm\buildmachine_++ue4+release-4.11\engine\source\editor\unrealed\private\filehelpers.cpp:2662]
UE4Editor_UnrealEd!FEditorFileUtils::SaveDirtyPackages() [d:\buildfarm\buildmachine_++ue4+release-4.11\engine\source\editor\unrealed\private\filehelpers.cpp:2776]
UE4Editor_ContentBrowser!ContentBrowserUtils::SaveDirtyPackages() [d:\buildfarm\buildmachine_++ue4+release-4.11\engine\source\editor\contentbrowser\private\contentbrowserutils.cpp:634]
UE4Editor_ContentBrowser!SContentBrowser::OnSaveClicked() [d:\buildfarm\buildmachine_++ue4+release-4.11\engine\source\editor\contentbrowser\private\scontentbrowser.cpp:1696]
UE4Editor_ContentBrowser!TMemberFunctionCaller::operator()<>() [d:\buildfarm\buildmachine_++ue4+release-4.11\engine\source\runtime\core\public\delegates\delegateinstanceinterface_variadics.h:161]
UE4Editor_ContentBrowser!TTupleImpl >::ApplyAfter_ExplicitReturnType >() [d:\buildfarm\buildmachine_++ue4+release-4.11\engine\source\runtime\core\public\delegates\tuple.h:128]
UE4Editor_ContentBrowser!TBaseSPMethodDelegateInstance<0,SContentBrowser,0,FReply cdecl(void)>::Execute() [d:\buildfarm\buildmachine++ue4+release-4.11\engine\source\runtime\core\public\delegates\delegateinstancesimpl_variadics.inl:321]
UE4Editor_Slate!TBaseDelegate::Execute() [d:\buildfarm\buildmachine
++ue4+release-4.11\engine\source\runtime\core\public\delegates\delegatesignatureimpl_variadics.inl:521]
UE4Editor_Slate!SButton::OnMouseButtonUp() [d:\buildfarm\buildmachine_++ue4+release-4.11\engine\source\runtime\slate\private\widgets\input\sbutton.cpp:273]
UE4Editor_Slate!::operator()() [d:\buildfarm\buildmachine_++ue4+release-4.11\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:4540]
UE4Editor_Slate!FEventRouter::Route >() [d:\buildfarm\buildmachine_++ue4+release-4.11\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:214]
UE4Editor_Slate!FSlateApplication::RoutePointerUpEvent() [d:\buildfarm\buildmachine_++ue4+release-4.11\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:4530]
UE4Editor_Slate!FSlateApplication::ProcessMouseButtonUpEvent() [d:\buildfarm\buildmachine_++ue4+release-4.11\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:4947]
UE4Editor_Slate!FSlateApplication::OnMouseUp() [d:\buildfarm\buildmachine_++ue4+release-4.11\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:4923]
UE4Editor_Core!FWindowsApplication::ProcessDeferredMessage() [d:\buildfarm\buildmachine_++ue4+release-4.11\engine\source\runtime\core\private\windows\windowsapplication.cpp:1415]
UE4Editor_Core!FWindowsApplication::DeferMessage() [d:\buildfarm\buildmachine_++ue4+release-4.11\engine\source\runtime\core\private\windows\windowsapplication.cpp:1732]
UE4Editor_Core!FWindowsApplication::ProcessMessage() [d:\buildfarm\buildmachine_++ue4+release-4.11\engine\source\runtime\core\private\windows\windowsapplication.cpp:697]
UE4Editor_Core!FWindowsApplication::AppWndProc() [d:\buildfarm\buildmachine_++ue4+release-4.11\engine\source\runtime\core\private\windows\windowsapplication.cpp:619]
user32
user32
UE4Editor_Core!FWindowsPlatformMisc::PumpMessages() [d:\buildfarm\buildmachine_++ue4+release-4.11\engine\source\runtime\core\private\windows\windowsplatformmisc.cpp:884]
UE4Editor!FEngineLoop::Tick() [d:\buildfarm\buildmachine_++ue4+release-4.11\engine\source\runtime\launch\private\launchengineloop.cpp:2610]
UE4Editor!GuardedMain() [d:\buildfarm\buildmachine_++ue4+release-4.11\engine\source\runtime\launch\private\launch.cpp:142]
UE4Editor!GuardedMainWrapper() [d:\buildfarm\buildmachine_++ue4+release-4.11\engine\source\runtime\launch\private\windows\launchwindows.cpp:126]
UE4Editor!WinMain() [d:\buildfarm\buildmachine_++ue4+release-4.11\engine\source\runtime\launch\private\windows\launchwindows.cpp:200]
UE4Editor!__scrt_common_main_seh() [f:\dd\vctools\crt\vcstartup\src\startup\exe_common.inl:264]
kernel32
ntdll

Thanks for the report! This crash was due to your level going over 2GB in size, and a piece of code that was still using a 32-bit size counter. We usually recommend using multiple streaming levels for a world of this size, as you simply wouldn’t be able to load this level on a 32-bit game exe.

This specific crash will be fixed for 4.12, although we can’t guarantee that there aren’t other crashes with using such large single levels, and we still don’t recommend having levels this large.

Ok thanks for your reply much appreciated