Загрузка файла с RegularExpressionValidator, не работающим с Firefox только IE

 public static List<string> DivideIntoPartitions(string stringToDivide, int partitions)
        {
            var parts = new List<string>(partitions);
            var len = stringToDivide.Length;

            if (len < partitions)
            {
                throw new ArgumentException("partitions should be less than length");
            }

            if (len % partitions == 0)
            {
                var eachSubstrLength = len / partitions;

                for (int i = 0; i < stringToDivide.Length; i += eachSubstrLength)
                {
                    parts.Add(stringToDivide.Substring(i, eachSubstrLength));
                }
            }
            else
            {
                var nextDivisibleNumber = len + (partitions - (len % partitions));
                var lengthOfLastSubstr = nextDivisibleNumber / partitions;
                var lastItem = stringToDivide.Substring((len - lengthOfLastSubstr));
                stringToDivide = stringToDivide.Remove((len - lengthOfLastSubstr));

                var chunksize = stringToDivide.Length / (partitions - 1);

                for (int i = 0; i < stringToDivide.Length; i += chunksize)
                {
                    parts.Add(stringToDivide.Substring(i, chunksize));
                }
                parts.Add(lastItem);

            }
            return parts;

        }

 var result = DivideIntoPartitions("qrstuvwxyz", 3);