There is a setting in SCLogin called 'Encrypt Login Form'. When this value is set to Yes, the form should be submitted over https. However, it seems like Joomla has a bug when using an IP address that the form gets sent via http. If you leave the value as No, the form will be submitted however the user is viewing the page. This will be as https if that's how they're viewing the page.
You can confirm this with the standard Joomla Login module, as it has the same setting and is calling the same Joomla methods that SCLogin is using.
We have re-set the value to No in the SCLogin module on your page and the login from our module now works.
-Melissa