Get player by name

[NiLSPACE]

Strange. I don't see a TakeDamage function that has a cEntity as first parameter. What I did notice though is that you're giving the position of the projectile entity. That should be a double.
Something like this:

Entity:TakeDamage(dtArrow, a_Player, 18, 4)

Also, please use

Code:

[shcode=lua][/shcode]

to post code. It's much more clearer