Validating norwegian number format

Question

So I have a little method that validates a number input based on the users browser culture. This is in asp.net webforms.

public static bool IsNumberInCulture(object source, EventArgs e) {
        TextBox validateSource = (TextBox)source;
        string validateThis = validateSource.Text.Trim();
        decimal result;

        if (validateThis.Length > 0) {
            if (decimal.TryParse(validateThis, NumberStyles.Number, UserCulture, out result)) {
                if (validateThis != result.ToString("N0", UserCulture) && validateThis != result.ToString("N1", UserCulture) && validateThis != result.ToString("N2", UserCulture)) {
                    return false;
                } else {
                    return true;
                }
            }
        }
        return false;
    }

This appears to work really well. Except with Norwegian numbers.

What is strange, is that the browser formats the number display correctly. Example. 6 000,00. If I delete and replace the numbers individually in the text box, the number validates to true. If I remove the number in the text box completely, and input a new number, using the same format (number, space, number, number, number, comma, number number) the number validates to false!!

I don't understand this. Anyone have any ideas?