site in question is at:
toughfloors.com/proto/gallery-epoxy-flooring.html

Put a lightbox gallery on it, and now client wants me to add more photos to it.

I can't seem to figure out how.

I get this error message
see this screen capture:
toughfloors.com/proto/gallery-epoxy-flooring.html

I see someone else had it in the forum, but the answer seemed specific to their site, so I couldn't figure out how to fix it.

To add to a gallery, I'm assuming I need to hit that Edit button in the dialog box that pops up, right? But I can't get that far because the error pops up

any ideas?

Hello John.

Can you please provide me with the correct link to your screenshot? Currently you had double posted the link to the page.

Regards:Vulcho.

Oh man, so sorry. Here's the link:

dl.dropbox.com/u/67658050/heightissue.png

Hello John.

Can you try to clear your Dreamweaver cache file ?
The following article will help you:
Clearing Dreamweaver's cache

Regards:Vulcho.