Is this only happening with the SCLogin module? Can you test with the standard Joomla login (mod_login) module to see if the same behavior happens with that? If so, then the issue isn't with the SCLogin module and there's likely not much we can do to help.
In general though, I'd double check the Login Redirection and Logout Redirection settings in the parameters of the module to ensure that they are set to a valid, public menu item.
I hope that helps,
Alex