[Mikkel_Pedersen]

A global boolean array to represent if player is jailed or not.

pawn Код:

new bool:IsJailed[MAX_PLAYERS];

To avoid bugs with players being jailed when connecting (if player is assigned a playerid, which was earlier jailed, you'll reset it when the player joins)

pawn Код:

public OnPlayerConnect(playerid)
{
    IsJailed[playerid] = false;
}

When you jail the player, you set it to true and check if the the player is already jailed.

pawn Код:

CMD:jail(playerid, params[])
{
    if(IsPlayerAdmin2[playerid] == 2)
    {
        new targetid, Text:JailTextDraw, reason[128], msg[64], name[46];
        if(sscanf(params, "us[128]", targetid, reason)) return SendClientMessage(playerid, COLOR_ORANGE, "USAGE: /jail [id] [reason]");
        if(!IsPlayerConnected(targetid)) return SendClientMessage(playerid, COLOR_WHITE, "That player is not online.");
        if(IsJailed[targetid] == true) return SendClientMessage(playerid, COLOR_WHITE, "That player is already jailed.");
        IsJailed[targetid] = true;
        GetPlayerName(playerid, name, sizeof(name));
        format(msg, sizeof(msg), "%s was jailed. Reason: %s. Time: 120sec.", name, reason);
        SendClientMessageToAll(COLOR_RED, msg);
        SetTimer("jailtime", 120000, false);
        SetPlayerInterior(targetid, 6);
        SetPlayerPos(targetid, 265.34756469727, 77.521759033203, 1001.0390625);
        JailTextDraw = TextDrawCreate(327.000000, 377.000000, "X");
        TextDrawAlignment(JailTextDraw, 2);
        TextDrawBackgroundColor(JailTextDraw, 255);
        TextDrawFont(JailTextDraw, 2);
        TextDrawLetterSize(JailTextDraw, 0.620000, 3.200000);
        TextDrawColor(JailTextDraw, -1);
        TextDrawSetOutline(JailTextDraw, 0);
        TextDrawSetProportional(JailTextDraw, 1);
        TextDrawSetShadow(JailTextDraw, 1);
        CountdownTextDraw(targetid, JailTextDraw, 120);
        return 1;
    }
    return 1;
}

Also, at your 'GetPlayerName' you are getting the playerid's name (AKA: The player who uses the command).
Should be:

pawn Код:

GetPlayerName(targetid, name, sizeof(name));

EDIT: Also don't forget to set IsJailed[playerid here] to 'false' when the player is unjailed (probably at your "jailtime")