If you are using any kind of firewall or personal proxy, please disable it and try to finish the registration process or the send/receive action.
If the problem persists, you will have to configure your Firewall to allow IncrediMail access to the Internet.
Go to the firewall settings, find the list of all the programs the firewall has detected and allow the following applications full access to the Internet:
This action should allow you to work with IncrediMail and your firewall at the same time.
For more information on configuring Firewalls, please check the following article:https://incredimail.zendesk.com/entries ... ncredimail