invalid length for a base 64 char array

Hi I have a code below, but everytime, my "text" throwing an error invalid length for a base 64 char array, and I don't know how to fix this.

Code:

---

try
            {
                key = Encoding.UTF8.GetBytes(stringKey.Substring(0, 8));
                DESCryptoServiceProvider des = new DESCryptoServiceProvider();
                Byte[] byteArray = Convert.FromBase64String(text);
                MemoryStream memoryStream = new MemoryStream();
                CryptoStream cryptoStream = new CryptoStream(memoryStream,
                    des.CreateDecryptor(key, IV), CryptoStreamMode.Write);
                cryptoStream.Write(byteArray, 0, byteArray.Length);
                cryptoStream.FlushFinalBlock();
                return Encoding.UTF8.GetString(memoryStream.ToArray());
            }
            catch (Exception ex)
            {
                // Handle Exception Here
            }
            return string.Empty;

---

Turned out there's a "+" sign in my string, but how to get rid of it? If I put any other characters, it will screw up my string though.

The proper way to get rid of it is to tackle it at its source. If it's coming in from a database then figure out what's putting it there and get that application to do it right.

The improper way is to perform a .Replace(), replacing the + with an empty string, but that doesn't guarantee future problems in the base64 string, since other characters may get introduced in there.