Club Log is regularly targeted by malicious parties, which is expected for a large web site. There are various automated measures in place to protect Club Log from abuse which would disrupt expeditions and other legitimate users.. Club Log automatically firewalls out traffic which is deemed to be a problem (the specifics of which are not described here).
If your application sends many requests to Club Log which result in error 403 (access denied) then your IP address will be automatically banned for a period of time.
If you have misconfigured your logging software and repeatedly attempt to upload QSOs using the realtime.php endpoint, this will cause an error 403 to be issued. It is highly likely this will result in your IP address being blocked if not corrected. If you are the author of a logging programme, please be sure to validate user credentials and handle error 403 appropriately, i.e. disable further upload attempts until valid credentials are supplied.
If you experience issues and cannot track them down, but think your IP address has been banned, please open a support ticket. The helpdesk is not blocked by the same processes and will remain available to you.