GetEntByNum() is one of those functions with a developer flag, they only work in a /# ... #/ comments like:
PHP Code:
/#
entity = clientNumToEntity( int(result[0]));
if(result[1]=="OK"){
entity iprintln("OK");
#/
Compiler will ignore everything under /# ... #/ comments unless developer_script is set to 1.
There is no performance impact on calling exec_async_checkdone every frame, well you can call it
not per frame maybe every 0.1 or something but you're gonna end up with slightly delayed callbacks then.