[TYPO3-english] FEuser dropped after first link

[Tony Lush]

When a FEuser logs in they are returned to the login page and can see 
additional content, including a link to a private page. When they follow 
any link, however, they get a Page Not Found error and are no longer 
logged in.

TYPO3 4.1.10 (recently upgraded from 4.1.7 to 4.1.8 to 4.1.10)
newloginbox 3.1.0
sr_feuser_register 2.5.8

Can anyone suggest where I might troubleshoot this?

Thank you -- Tony Lush