If you are getting this error message when trying to connect to cPanel or Webmail there are several things to try to solve this issue. This is usually due to using some kind of proxy or VPN that changes your IP address every few seconds/minutes. Another reason might be if your ISP constantly changes your IP addresses.
For CPanel:
- Try to access cPanel like this http://cpanel.mydomain.com , sometimes that will fix things.
- In WHM's Tweak Settings, change the setting "Cookie IP validation" from Strict to Loose.
- Change the proxy/VPN you are using to one which doesn't changes your IP address.
For Webmail: Try to access Webmail like this http://webmail.mydomain.com instead of http://mydomain.com/webmail, sometimes that will fix things.
Note: If Using ssl make sure you start with https:// instead of http://
