Happens to me as well, on a non-animated polygon collider.
Actor::updateMassFromShapes: Compute mesh inertia tensor failed for one of the actor's mesh shapes! Please change mesh geometry or supply a tensor manually!
UnityEngine.GameObject:AddComponent()
tk2dBaseSprite:CreateCollider() (at Assets/TK2DROOT/tk2d/Code/Sprites/tk2dBaseSprite.cs:556)
tk2dBaseSprite:EditMode__CreateCollider() (at Assets/TK2DROOT/tk2d/Code/Sprites/tk2dBaseSprite.cs:616)
tk2dBaseSprite:ForceBuild() (at Assets/TK2DROOT/tk2d/Code/Sprites/tk2dBaseSprite.cs:648)
tk2dSprite:ForceBuild() (at Assets/TK2DROOT/tk2d/Code/Sprites/tk2dSprite.cs:230)
tk2dSpriteCollectionBuilder:RefreshExistingAssets(tk2dSpriteCollectionData) (at Assets/TK2DROOT/tk2d/Editor/Sprites/tk2dSpriteCollectionBuilder.cs:1210)
tk2dSpriteCollectionBuilder:Rebuild(tk2dSpriteCollection) (at Assets/TK2DROOT/tk2d/Editor/Sprites/tk2dSpriteCollectionBuilder.cs:1162)
tk2dSpriteCollectionEditorPopup:Commit() (at Assets/TK2DROOT/tk2d/Editor/Sprites/SpriteCollectionEditor/tk2dSpriteCollectionEditorPopup.cs:437)
tk2dSpriteCollectionEditorPopup:DrawToolbar() (at Assets/TK2DROOT/tk2d/Editor/Sprites/SpriteCollectionEditor/tk2dSpriteCollectionEditorPopup.cs:427)
tk2dSpriteCollectionEditorPopup:OnGUI() (at Assets/TK2DROOT/tk2d/Editor/Sprites/SpriteCollectionEditor/tk2dSpriteCollectionEditorPopup.cs:826)
UnityEditor.DockArea:OnGUI()
The thing is, it did not happen for a while, then it started happening, and it does not go away.
( Unity 3.5, Toolkit 1.92 final + patch 1 )