Too many IP addresses accessing one secure area

I'm suddenly getting this error when trying to login to my s2Member protected site:
503: Service Temporarily Unavailable
Too many IP addresses accessing one secure area!
Please contact Support if you need assistance.
I've verified that this is a problem with s2Member by
1. Disabling all other plugins except s2Member
2. Switching to a different theme with only s2Member active
The error only occurs when trying to login to the site. Also, it seems to work fine for some users - my web hosting support tech managed to login with no problems while I wasn't able to login at the same time. Also, I'm not sure if it's relevant but I have used the Capability Manager plugin to create custom roles for my site.
The error is here: http://clientarea.clickwp.com/wp-login.php
Username: johndoe
Password: qwe123
Thanks
503: Service Temporarily Unavailable
Too many IP addresses accessing one secure area!
Please contact Support if you need assistance.
I've verified that this is a problem with s2Member by
1. Disabling all other plugins except s2Member
2. Switching to a different theme with only s2Member active
The error only occurs when trying to login to the site. Also, it seems to work fine for some users - my web hosting support tech managed to login with no problems while I wasn't able to login at the same time. Also, I'm not sure if it's relevant but I have used the Capability Manager plugin to create custom roles for my site.
The error is here: http://clientarea.clickwp.com/wp-login.php
Username: johndoe
Password: qwe123
Thanks