cPanel will sometimes throw out the error "IP address has changed!" while you trying to connect.
Some ISPs are have very short DHCP life times. This can cause the behavior described and these types of connections could not work with cPanel. You can try several things to try to fix the issue:
1) Going to http://cpanel.mydomain.com as sometimes that will fix things.
2) cPanel and WHM version 11.28 have a new option to the Cookie IP validation setting:
"Validate the IP addresses used in all cookie based logins. This will limit the ability of attackers who capture cPanel session cookies to use them in an exploit of the cPanel or WebHost Manager interfaces. For this setting to have maximum effectiveness, proxydomains should also be disabled."
Change this setting to "loose" and it should cause the reauthentication frequency to diminish or go away. To disable it go to WHM > Tweak Settings > Cookie IP validation and set it to "loose"
3) Otherwise, you might have utilize a proxy with an unchanging IP
4) If you're still getting those error messages, you will need to find another connection to connect into cPanel.