As far as I know, the ID being passed to your "show_message" function will be the same as the Task ID, which you put as:
TASK_ID+id, but then you try to use that ID in the show_message function as if it were a player ID.. I think you should minus TASK_ID from the player ID first..
Code:
#include <amxmodx>
public plugin_init()
register_plugin("HUD Score","0.1","v3x")
#define TASK_ID 2934
public client_connect(id) set_task(1.0,"show_message",TASK_ID+id)
public client_disconnect(id) remove_task(TASK_ID+id)
public show_message(id) {
new playerID = id - TASK_ID
new frags = get_user_frags(playerID)
new deaths = get_user_deaths(playerID)
new msgstr[64]
format(msgstr,63,"Kills: %i / Deaths: %i",frags,deaths)
set_hudmessage(255,255,255,-1.0,0.35,2,0.1,1.0,0.02,0.02,10)
show_hudmessage(playerID,msgstr)
return PLUGIN_HANDLED
}
I hope that helps, or even works!