Gallery Theme copied on codebase site and now themes cant be changed

I have Gallery2 installed and working just fine. Managed to make the site look great, making changes to template which is x_treme.

I had also managed to make a multisite, as per documents. All was working OK, except I needed to change a logo and inf. on the new site to suit the new website. Reading though the documents, I read that I would not be able to change template in new website install. It does not have template files etc. So I downloaded a copy of my altered xtreme template and then uploaded it back to the server - hoping that I could then change it in the newsite admin themes after making changes to it.

However before I made any changes to the new copied template, I tested my theory and could not open the themes section in the admin area on either the new site or the codebase site.

Anyone know what I did wrong please, desperate to get my theme back working again, took me hours to do.