Update you addons, that issue was fixed quite some time ago.
It's EXTREMELY hard to tell when ace addons are updated these days. The curse date listed is for svn commits, not release versions, and I've been updating manually. I'll update both again and see if it's fixed, but 'quite some time ago' is inaccurate. My last update run was no less than 5 days ago.
I'm not sure why or when i'm getting that error but sometimes it just show up
any idea what is causing that ?
Interface\FrameXML\UnitFrame.lua:159: Usage: GameTooltip:SetUnit("unit"):
Interface\FrameXML\UnitFrame.lua:159: in function `UpdateTooltip':
Interface\FrameXML\GameTooltip.lua:171: in function `GameTooltip_OnUpdate':
<string>:"*:OnUpdate":1: in function <[string "*:OnUpdate"]:1>