Some Tips:  Session problems are often temporary and can sometimes correct themselves.  If you have your browser set to allow session cookies within your browser's privacy settings, here are other things to look for:

Too Many Windows - Sometimes, having a lot of browser windows or tabs opened can cause your browser to start acting up.  Try closing some tabs and/or restarting your browser to see if that corrects the issue.

Low Memory - Just like above, too many windows opened or software programs running can cause low memory.  Try closing some things.  Also, if it has been a while since you've rebooted your computer, now would be a good time to do that.

Multiple Accounts - If you have multiple ClixTrac accounts, it's possible your stored sessions are being mixed up.  Use the 'Log Out' link in your control panel to make sure your account fully logs out.  This will help ensure your previous session is removed before logging back in.

Password Storing - Most browsers allow you to store passwords to make it easier to log in later.  Make sure that if you're using that feature you haven't changed your password since it was last stored.  The conflicting passwords will most likely cause login issues.

Session Restore - Some browsers allow you to restore previously closed sessions upon restarting your browser.  Doing so might cause it to use an expired session.  Use the 'Log Out' link in your control panel to remove any invalid session before trying to log back in.