"；标准表达式“”中的数据类型不匹配；在C#中

我在字符串变量中有一个数字"userID"。我正在将其转换为int，以从数据库中获取"用户名"answers"角色"，该数据库有一个具有AutoNumber数据类型的"user_ID"字段。转换后的userID被分配给变量"value"。但我在行中得到了"标准表达式中的数据类型不匹配"

OleDbDataReader roleReader = command.ExecuteReader();

这是的完整代码

class HomeClass
{
    string userID;
    string role;
    string username;
    public HomeClass(string myUserID)
    {
        userID = myUserID;
    }
    public string checkRole()
    {
        int value;
        value = Int32.Parse(userID);
        string query = "SELECT role FROM userAccounts WHERE user_ID = '" + value + "'";
        ConnectDatabaseString myConnectionString = new ConnectDatabaseString();
        OleDbConnection connection = new OleDbConnection();
        connection.ConnectionString = myConnectionString.connect();
        connection.Open();
        OleDbCommand command = new OleDbCommand();
        command.Connection = connection;
        command.CommandText = query;
        OleDbDataReader roleReader = command.ExecuteReader();
        roleReader.Read();
        role = roleReader["roles"].ToString();
        return role;
    }
    public string getUsernameToBeShown()
    {
        int value;
        value = Int32.Parse(userID);
        string query = "SELECT username FROM userAccounts WHERE user_ID = '" + value + "'";
        ConnectDatabaseString myConnectionString = new ConnectDatabaseString();
        OleDbConnection connection = new OleDbConnection();
        connection.ConnectionString = myConnectionString.connect();
        connection.Open();
        OleDbCommand command = new OleDbCommand();
        command.Connection = connection;
        command.CommandText = query;
        OleDbDataReader usernameReader = command.ExecuteReader();
        usernameReader.Read();
        username = usernameReader["username"].ToString();
        return username;
    }
}

这个错误的根本原因是什么？