CB 2.43
Install the latest CB build release. Next ensure all your installed CB plugins are up to date. Fastest way to do this is use the Update All feature within CB > Plugin Management > Install New Plugin > Install from Web.
Are you able to reproduce the issue with a test user? Is there any more details about the error within your server error log? This usually happens when something alters the $user object and nulls it or tries to act on it before it has been established.