I'm getting this very error when registering a new user in Sharepoint 2010 (FBA) using asp:CreateUserWizard. For already existing users, the FBA login process works just fine.
When I run the registration.aspx page that time the wizard brings up the success page with the "Continue" button. and existing users able to accessing all pages but when user going to sign out On Personal action link. got erros
Exception of type 'System.ArgumentException' was thrown. Parameter name: encodedValue
that time i have clear all cookies from browser than work as fine..but when second time I am create User in Registration.aspx page facing same issue again..