because razor's code isn't directly integrated into the client code. Think of razor as a tape player that is repeating the same commands over and over again, the client will do what it says but only as fast as it can. if you say two commands to the client faster than the client can execute them, it will completely ignore that second command and execute the next available command that it has time to execute.
for example
lets say that your client (just for arguments sake) can only execute one command every second, if you having razor give the client commands every half a second, only every other command will register.
spell macro from client
last spell
wait for target
last target
and cast a harmful spell over another target at the same time
this is where your problem is, if you simply fix your timing you will correctly cast the harmful spell and your vet on their respective targets. I would suspect that you would be seeing another error besides "you cannot perform beneficial acts on that" I would suspect that you are also seeing an error from trying to cast a harmful spell on your pet. either that or you are successfully casting the harmful spell on your pet
try changing your "wait for target"(s) to wait for X milliseconds for a quick and dirty fix
