Question : Invalid length for a Base-64 char array

I open a web page with the following URL and query string :

https://myurl.com/print.aspx?PN=lvAg6+P2/4Q=&PW=650

On page load I get the following erorr:

Invalid length for a Base-64 char array.

Any help on cause of this error would be rgeatly appreciated. Is there anything to do with the query string?
Thanks in advance

Answer : Invalid length for a Base-64 char array

You may also need to do a Server.UrlEncode(text) before adding it to the querystring, I can't remember for sure.