Invalid length for a Base-64 char array

This error gave me when i try to encrypt the query string. I solved this issue by http://forums.asp.net/t/1222829.aspx.
It worked fine. But now for some query string values it gives same error. The reason is there was a space character in the query string value. Then i replaced space character with "+". Its working now.

64-bit encoding does not work well with spaces in the string for some odd reason.