Is there a way to select an album thumbnail from a sub album 2 levels deeper? Can't figure out how to do it, the image I want does not show in dropdown

You have to enable the option to show subalbum thumbnails in the gallery options. This is not defaulted because often it is too much overhead for some servers to enumerate all the subalbum images.

I already had that enabled, still only showing the thumbs from the first subalbums, nothing from the 3rd level.

This gallery has 7500 images. When I refresh the database (using FF) the window appears to flash & never completes. The window tab keeps flashing "connecting". Am I not allowing enough time? Is that possibly the problem?

Please read: http://www.zenphoto.org/news/why-are-some-of-my-thumbnails-sized-images-not-generated-why-does-zenphoto-make-my-server-crash-while-processing-images-

Also this might be why the option is not normally enabled. If your site cannot handle the processing your only option is to manually change the database.

Just to make myself clear. I don't want to show the subalbum thumbnail "images" in the drop down list. Just the text listing.

The subalbums all list the thumbnails, so I know the database has collected the data. But that data is not being added to the list. The list could get very long, I realize that.

So....your saying that even just a text list of sub-subalbum file names is too taxing on the server??

I actually tried the option to show the thumbnail 'images' in the drop down menu, and that did work fine, one level deep only.

Out of curiosity, I added some sub level albums to a an existing small album. The total tree (all 3 levels) only contains 245 images. There are 4 images in 2 bottom level albums (just 2 images per album). These 4 images refuse to show up in the thumbnail selector for the top level album.

The database updated no problem, taking only seconds.

It of course matters how big the list--that is why it is an option. The option you want is not the "show images" option. It is the option I already mentioned above.