Replace invalid characters with Regular Expression

The code snippet below replaces all invalid characters for a filename with Regex’ static Replace method;

/// <summary>
/// Replaces invalid path/file characters in given string with an underscore
/// </summary>
/// <param name="getString">string array to get string from CTX-Release</param>
/// <param name="lParamCount">number of parameteres which is set by CTX-Release while calling the function</param>
/// <returns>string with invalid characters replaced with underscore</returns>
public string ReplaceInvalidPathChars(object[] getString, int lParamCount)
{
    string retValue = String.Empty;
    if (getString.Length > 0)
    {
        retValue = getString[0].ToString();
        char[] invalidChars = System.IO.Path.GetInvalidFileNameChars();                
        string invalidString = Regex.Escape(new string(invalidChars));
        retValue = Regex.Replace(getString[0].ToString(), "[" + invalidString + "]", "_");
        retValue = retValue.Replace(" ", "_");
    }
    return retValue;
}

(Source: C# in a Nutshell by Albahari)