What steps will reproduce the problem?
1. Install CowTip.
2. Enter any Arena.
3. Mouse-over any enemy player.

What is the expected output? What do you see instead?
I expected to see the same result that PitBull showed on my target frame for the tags that I use in both addons, e.g. HP or Name.
Instead I got "arenaX is not a valid unit id" (something along that) in any line.

What version of the product are you using?
LibDogTag-Unit-3.0 r165 was the last version that I played arena with.
Will update to newest version and update this ticket as soon as I played arena again.

Do you have an error log of what happened?
Unfortunately not.