This occurs in Classic Era using TitanPanel when requesting a menu (right-click).
Using the same TitanPanel code in WOTLK Classic does not produce this error.
Some menus appear anyway, some do not appear at all.
36x SharedXML/SharedUIPanelTemplates.xml:1474 Texture Texture: Unable to load atlas entry UI-Frame-DiamondMetal-Header-CornerRight
36x SharedXML/SharedUIPanelTemplates.xml:1480 Texture Texture: Unable to load atlas entry _UI-Frame-DiamondMetal-Header-Tile
48x SharedXML/SharedUIPanelTemplates.xml:1468 Texture Texture: Unable to load atlas entry UI-Frame-DiamondMetal-Header-CornerLeft
I could not find any reference to this in Titan nor Ace libs used nor exported code.
Any tips to resolve this would be appreciated!
The Atlas will be a Blizzard thing from a template primarily used by the Blizzard_Calendar addon which is not a Classic_Era thing.
I did find it in the exported CE code… so why is it sprinkled throughout in CE WoW files?
Guessing Ace3 uses one (in)directly?
C:\Software\World of Warcraft_classic_era_\BlizzardInterfaceCode\Interface\SharedXML\NineSliceLayouts.lua
C:\Software\World of Warcraft_classic_era_\BlizzardInterfaceCode\Interface\SharedXML\SecureUIPanelTemplates.xml
C:\Software\World of Warcraft_classic_era_\BlizzardInterfaceCode\Interface\AddOns\Blizzard_BehavioralMessaging\Blizzard_BehavioralMessaging.xml
C:\Software\World of Warcraft_classic_era_\BlizzardInterfaceCode\Interface\SharedXML\SharedUIPanelTemplates.xml
The UI-Frame-DiamondMetal-Header-CornerLeft etc. atlases are only in the DialogHeaderTemplate which is only used in the actual game code in the Blizzard_Calendar addon and the code to load that is only UIParent.lua file that is listed in the Interface_Wrath folder. There are various calls to load the calendar in various places but they all lead back to code in the “Interface_Wrath” folder (exported from 1.14.4 build 51311).
Why is Blizz. including folders for TBC and Wrath code in Vanilla? I’m sure there’s an explanation somewhere, just maybe no available to the public 
Thank you! Your mention of Calendar (twice!) triggered a memory. Long before I touched Titan there has been a hack that forces load of the Blizzard_Calendar when building a right click menu to ‘force init of drop down buttons’. Commented out - no error.
As to side effects… 
Thanks again.