There was a problem logging onto your mail server.
Your username was rejected. Account: 'pophost.123-reg.co.uk.co.uk', Server: 'pop3.norton.antivirus', Protocol: POP3, Server Response: '-ERR', Port: 110, Secure(SSL): No, Server Error: 0x800CCC90
This error message is caused by the fact that you have set an anti-virus program to scan all emails automatically (in the above case, it is Norton AntiVirus). Changing your email client settings will not solve the issue. You need to go into your anti-virus program and change the scan setting there.