First, this plugin is outstanding.. Hats off to Alex!
Two problems - I think I've resolved the first one - but I'm not sure that it isn't part of the second, so I'll describe it.
Background - my hosting company, bluehost, who are generally excellent - has three available gallery applications (coppermine, 4images and Gallery2) in its ready-to-install Fantastico open-source menus. I wanted to do more with images in my blogs - tried all three. All had problems with 777 permissions. Bluehost was, for the first time, disappointing. First they said they'd been hearing a lot about this - put a "Level 3" (highest level) person on it - they'd fix it. (Still haven't heard back from that guy).
So I found NextGen by searching for a plugin. In my sandbox site, worked fine.
Put in one of my working blogsites - got 777 permission errors. After Bluehost (different tech support crew by then, a day later) they said the couldn't do anything about it.
So I changed the permissions to 777 by right-clicking the folders I'd created as per the plugin.
NextGen started working perfectly.
Finally (where we are now) All the preview pictures of my themes are not visible - the themes won't load - and I'm now deactiving plugins, reloading, rebooting, try to get down to where I isolate the problem.
Any thoughts, suggestions, happily accepted. Depending on budget, willing to pay or barter for assistance. I'd really like this plugin - but I want the rest of WP working as well.