[wups]

You should also return the Armour.

pawn Code:

if(HealthLost > 0.0)
{
     new Float:hp;
     GetPlayerHealth(Target, hp);
     SetPlayerHealth(Target, hp + HealthLost); 
}
if(ArmourLost > 0.0)
{
     new Float:Armour;
     GetPlayerHealth(Target, Armour);
     SetPlayerHealth(Target, Armour + HealthLost); 
}