This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
You don't tell us what's happening, or in which line of code it's happening, but usually this exception is caused by treating encrypted data (which is binary data) as character data (by storing it in a String object). The code seems to be doing exactly that.