WowAce

What steps will reproduce the problem?
1. login game

Do you have an error log of what happened?
1x AceHook-3.0-5 (ClassLoot):180: Attempting to rehook already active hook OnTooltipSetItem.
AceHook-3.0-5 (ClassLoot):180: in function <...ce\AddOns\ClassLoot\Libs\AceHook-3.0\AceHook-3.0.lua:118>
AceHook-3.0-5 (ClassLoot):370: in function `HookScript'
ClassLoot-v1.7.3\ClassLoot.lua:114: in function `HookTip'
ClassLoot-v1.7.3\ClassLoot.lua:103: in function `HookTooltips'
ClassLoot-v1.7.3\ClassLoot.lua:92: in function <ClassLoot\ClassLoot.lua:89>
(tail call): ?:
<in C code>: ?
<string>:"safecall Dispatcher[1]":9: in function <[string "safecall Dispatcher[1]"]:5>
(tail call): ?:
AceAddon-3.0-10 (Ailo):543: in function `EnableAddon'
AceAddon-3.0-10 (Ailo):635: in function <...rface\AddOns\Ailo\Libs\AceAddon-3.0\AceAddon-3.0.lua:621>
<in C code>: in function `LoadAddOn'
Interface\FrameXML\UIParent.lua:244: in function `UIParentLoadAddOn':
Interface\FrameXML\UIParent.lua:318: in function `TimeManager_LoadUI':
Interface\FrameXML\UIParent.lua:519: in function <Interface\FrameXML\UIParent.lua:494>:

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I can only assume this is a conflict with another addon you are using as I can't see any way the tooltip scripts could try and be hooked twice. Running all my usual addons and only running ClassLoot with no other addons does not present this error.

Perhaps a list of installed addons might help pinpoint it.