What happened when you tried my previous suggestion about editing the constants file? Did svManager succeed in changing the permissions on the new gallery directory (g1 or whatever)? Did you get any error messages?
I'm finding it quite hard to understand what's happening on your server. I think I can work out what's happening when you create the first gallery. SvManager creates the svmanager/g1 directory and the permissions are determined by a setting called umask on your server. Your hosting organisation may or may not allow you to change umask.
The files and directories inside the gallery directory are not created from scratch but copied from the master gallery directory. This is either svmanager/svmaster or svmanager/plugins/simpleviewer/svmaster, depending on the version of svManager you are running. Presumably the 0755/0666 permissions you are seeing inside g1 are copied from the master.
The 500 error probably occurs because your server doesn't like the 0777 setting on the g1 folder – even though the server (perversely) created that setting itself. I have seen one or two servers before that are set up in this rather odd way.
The inconsistent behaviour on creating the g2 gallery is a total mystery to me. SvManager creates g2 in exactly the same way as g1 so I can't see why it should be different.
So, you could take a look at the permissions on the master directory and see if tweaking them makes a difference. You could double-check that there are no mistakes in your edits to the constants.php file, such as a missing zero in front of the permissions or incorrect quote marks. You could ask your server admin/helpdesk if there is any way to control the permissions on new directories created by a php script. After that I'm running out of ideas.
SimpleViewer Support Team.