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C#: System.ArgumentException '.', hexadecimal value 0x00, is an invalid character.

Yesterday my client reported one issue she was facing on production server while generating excel file.

Exception read as: “System.ArgumentException '.', hexadecimal value 0x00, is an invalid character”

After further investigation I was able to replicate and exception is thrown due to one string with troublesome characters (i.e. control and non-UTF-8 characters).

I have created one function (RemoveInvalidCharacters) to remove all the control and non-UTF-8 characters, and successfully removed all the troublesome characters.

/// <summary>
/// Method to remove control characters and other non-UTF-8 characters
/// </summary>
/// <param name="inputStr">The string to process</param>
/// <returns>String with no non-UTF-8 characters</returns>
public static string RemoveInvalidCharacters(string inputStr)
    if (inputStr == null) return null;

    var formattedStr = new StringBuilder();

    foreach (var ch in inputStr)
        // remove all control characters and non-UTF-8 characters as all.
        // except tabs and new lines
        if ((ch < 0x00FD && ch > 0x001F) || ch == '\t'
            || ch == '\n' || ch == '\r')

    return formattedStr.ToString();

Hope this solution helps you J

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