If you are frequently forcibly signed out of this site with the following error (or something like it):
Status: your IP address "X.Y.Z.W" differs greatly from the IP address used to first sign in. Please sign in again.
then follow these steps to fix the problem:
Sign in and go to Control Panel -> My Profile -> Preferences -> Advanced Session Preferences.
Scroll down the bottom of the page.
Under "IP Restrictions", choose "Allow Any IP Address".
Click "Save Data"
By toggling that preference, we will no longer expect you to arrive from the same set of IP addresses during a session. Most Internet users have the same IP for the duration of their browsing session, and visits from other IPs indicate problem, which is why we forbid this by default. However with certain Internet Service Providers, notably AOL, the normal operation is for users to bounce between a wide range of IP addresses during a normal session, and so this special handling is needed.
Please contact us if you repeatedly receive this error even after changing the setting above.