I just received this little problem today using my phone. It keeps logging me out with the following

Your IP address does not match this session

been using the same phone for weeks on end.

That's happening only in the ACP or?

That's a security feature, which can be disabled in your Security Center ( ACP => System => Security ) At top of the page there's a Security Settings Link and on this page disable the "Check IP address when validating session?" setting

just in the ACP. I probably will disabled it. But is it possible to be a risk. Security is my number one priority