When to use SqlConnection.ClearAllPools() in c#

I've noticed that my code errors out on sqlWrite.ExecuteNonQuery(); after executing 200 Insert queries in couple of seconds. I always thought that using will make sure the resources are reused properly and there will be no need to do anything. This is the first time I get this error and I've been dealing with sql/c# for almost 3 years doing different things.

using (SqlConnection varConnection = Locale.sqlConnectOneTime(Locale.sqlDataConnectionDetails)) 
{
    using (var sqlWrite = new SqlCommand(preparedCommand, varConnection)) 
    {
        sqlWrite.Parameters.AddWithValue("@var_agr_fname", var_agr_fname == "" ? (object) DBNull.Value : var_agr_fname);
        sqlWrite.ExecuteNonQuery();
    }
}


public static SqlConnection sqlConnectOneTime(string varSqlConnectionDetails)
{
    var sqlConnection = new SqlConnection(varSqlConnectionDetails);
    try
    {
        sqlConnection.Open();
    }
    catch
    {
        DialogResult result = MessageBox.Show(new Form {TopMost = true},
                                              "Błąd połączenia z bazą danych. Czy chcesz spróbować nawiązac połączenie ponownie?",
                                              "Błąd połączenia (000001)",
                                              MessageBoxButtons.YesNo,
                                              MessageBoxIcon.Stop);
        if (result == DialogResult.No)
        {
            if (Application.MessageLoop)
            {
                Application.Exit(); // Use this since we are a WinForms app
            }
            else
            {
                Environment.Exit(1); // Use this since we are a console app
            }
        }
        else
        {
            sqlConnection = sqlConnectOneTime(varSqlConnectionDetails);
        }
    }
    return sqlConnection;
}

Error message: A transport-level error has occurred when sending the request to the server. (provider: Shared Memory Provider, e