Error: Usage: UnitIsUnit("unit", "otherUnit")
AddOn: LunaUnitFrames
File: Tags.lua
Line: 701
Count: 2x

After casting a heal on my target.

Should be gone since 2.0

I have also gotten this error somehow:

Error: attempt to index field `?' (a nil value)
File: ...ns\LunaUnitFrames\libs\HealComm-1.0\HealComm-1.0.lua
Line: 1052
Count: 6

The first one is fixed in the next update. My guess about the second one is that its lag related. Needs more research.