Restore image binding error in C# windows application

I am creating windows application using c# 2010, in my application I am upload a image to database using image data type. Once stored is success (it’s working good) after that again I am bind a image, that time below error is came in first line

The input is not a valid Base-64 string as it contains a non-base 64 character, more than two padding characters, or a non-white space character among the padding characters.

  byte[] imageBytes = Convert.FromBase64String(base64String);
 MemoryStream ms = new MemoryStream(imageBytes, 0, imageBytes.Length);

How to solve this error, any one give me ideas.