problem with the sign up page

[hamza Hassan]

HI, i just started using Portofino so far have been able to set up the user management segment using tables i created on PostgreSQL but somehow am having problem with the sign up page. when i tried to sign up a new user i get an error message saying "com.manydesigns.portofino.shiro.User can not be cast to Serializable"  but the main issue is that when i check my database i can see the new user been inserted and am even able to login with the user which is why am not sure where and why the error is concurring