When experiencing this problem, there is a common fix for it. To fix this problem, do the following:
1) Click "Profile" in the navigation bar at the top of the page.
2) Enter a new password into the password box.
3) Click "Submit Changes" to change your password.
4) Click "Logout" to sign out of the site.
5) Log back into the site using your new password.
Once these steps have been taken, you shouldn't experience that problem any longer.