无法将带有[]的索引应用于类型为的表达式

我收到这个错误

Error   3   Cannot apply indexing with [] to an expression of type 

我的问题在这里

if (client["banhours"] == 0)
{
    client["banhours"] = -1;
    client["banreason"] = "Infinite time.";
    client["banstamp"] = DateTime.Now.AddYears(100);
}
if (Account.State == Database.AccountTable.AccountState.Banned)
{
    if (client["banhours"] != -1)
    {
        DateTime banStamp = client["banstamp"];
        if (DateTime.Now > banStamp.AddDays(((int)client["banhours"]) / 24).AddHours(((int)client["banhours"]) % 24))
            Account.State = Database.AccountTable.AccountState.Player;
    }
}

客户端是>>Client.GameClient客户端；