Code:
warning 201: redefinition of constant/macro (symbol "e_COMMAND_ERRORS")
C:\Users\iwanmf\Desktop\AG-RP\gamemodes\afera.pwn(1428) : error 021: symbol already defined: "COMMAND_ZERO_RET"

enum e_COMMAND_ERRORS
{
    // The majority of these are even - odd numbers return "1" not "0".
    COMMAND_ZERO_RET      = 0 , // The command returned 0.
    COMMAND_OK            = 1 , // Called corectly.
    COMMAND_UNDEFINED     = 2 , // Command doesn't exist.
    COMMAND_DENIED        = 3 , // Can't use the command.
    COMMAND_HIDDEN        = 4 , // Can't use the command don't let them know it exists.
    COMMAND_NO_PLAYER     = 6 , // Used by a player who shouldn't exist.
    COMMAND_DISABLED      = 7 , // All commands are disabled for this player.
    COMMAND_BAD_PREFIX    = 8 , // Used "/" instead of "#", or something similar.
    COMMAND_INVALID_INPUT = 10, // Didn't type "/something".
}
forward e_COMMAND_ERRORS:OnPlayerCommandPerformed(playerid, cmdtext[], e_COMMAND_ERRORS:success);
public e_COMMAND_ERRORS:OnPlayerCommandReceived(playerid, cmdtext[], e_COMMAND_ERRORS:success)
{
    if(success != COMMAND_OK)
    {
        new string[128];
        format(string, sizeof(string), "{030CDE}[SM] {FF0000}Command %s doesn't exist !", cmdtext);
        SendClientMessage(playerid,-1, string);
        return COMMAND_OK;
    }
    return COMMAND_OK;
}