Judging by this log I would say they never thought of a GPU having over 2Gigs of ram so with 3Gigs it reports it as -1Gig.
Audio devices: Generic Hardware (default: Generic Hardware)
Player: init engine
Direct3D:
Version: Direct3D 9.0c [aticfx32.dll 8.17.10.1230]
Renderer: AMD Radeon HD 7900 Series
Vendor: ATI
VRAM: -1024 MB
D3D: VRAM amount suspiciously low (less than 32MB for PS2.0 card)
desktop: 1920x1080 60Hz; virtual: 1920x1080 at 0,0
Checking for udpates
UnityEngine.Debug:Log(Object)
VersionUpdater:checkUpdateAsync()
VersionUpdater:Awake()
(Filename: \unitybuild\unity\Runtime\Export\Generated\BaseClass.cpp Line: 1651)
Stacktrace:
at (wrapper managed-to-native) UnityEngine.Graphics.Internal_DrawMeshNow1 (UnityEngine.Mesh,UnityEngine.Vector3,UnityEngine.Quaternion,int) <0x00004>
at (wrapper managed-to-native) UnityEngine.Graphics.Internal_DrawMeshNow1 (UnityEngine.Mesh,UnityEngine.Vector3,UnityEngine.Quaternion,int) <0xffffffff>
at UnityEngine.Graphics.DrawMeshNow (UnityEngine.Mesh,UnityEngine.Vector3,UnityEngine.Quaternion,int) <0x00042>
at UnityEngineInternal.ImposterRenderTexture.UpdateImposter (UnityEngine.Camera,UnityEngine.Light[],UnityEngine.Rect,UnityEngineInternal.TreeDatabase/Prototype) <0x003d7>
at UnityEngineInternal.ImposterRenderTexture.UpdateImposters (UnityEngine.Camera,UnityEngine.Light[]) <0x002a5>
at UnityEngineInternal.TreeRenderer.Render (UnityEngine.Camera,UnityEngine.Light[],single,single,single,int,bool,int) <0x00a60>
at UnityEngine.Terrain.CullAllTerrains () <0x009b8>
at (wrapper runtime-invoke) UnityEngine.StackTraceUtility.runtime_invoke_void (object,intptr,intptr,intptr) <0xffffffff>
Receiving unhandled NULL exception
Trying to recover from null exception