Ricky Y , I have experienced this as well . I have also noticed when that happened that I also had to re-login to other things .

In my experience , this was caused by some bug that I got from browsing other sites . The bug would clear out one's saved logins to any site . Thus requiring you to re-enter your login info , whereby the bug would capture your login info in an effort to steal your identity .

When this happens , do a security scan with whatever security software you have ( Norton , Spyware , etc . ) and once you have completed that , the constant request to login should go away .

Anytime you experience an " odd " request to re-login to sites that you have always been able to access without doing the constant login , it's generally a sign that one has picked up an identity bug that wants to capture your login info . The bug doesn't discern between an XMarks login or a credit card or an email login , it just looks for login info .

I have learned that when I try to click on my XMarks icon on my desktop and then all of sudden it doesn't recognize me ( or any other pre-saved login site ) that I have an identity bug that I accidentally picked up somewhere . So at that point I do a scan and clear out the problem .

On the other hand , if you are talking about going on the XMarks site and never closing out when you are done , then the site will time you out .

However , from your comments , it would seem that you are not talking about a time out .

Hope this helps .

Cheers , Mike