For some reason, my albums will not sort manually. I checked the option is on manual sort but when I try dragging them into a specific order, I get this error: Album already exists.

I cannot reproduce any issue with the sorting. This could happen if you try to make an album a subalbum but an subalbum of that name already exists. Then you have to rename it first.

It's a weird error. I seem to be able to sort the root albums of the gallery just fine. It just will not sort any subalbums. All the albums names are unique.

Check the server error log, could be a permissions issue.

I'm running it locally but there's no php errors in the log. I do actually have two installations of zenphoto running for two separate sites. The first is small, only about 200 images and you can sort all the subalbums just fine in that. The other one has like 15,000 images and a few hundred albums.

Well, as a last resort, I emptied the albums table in phpmyadmin and it has fixed the problem.

Kinda worrying though that this could happen again.

If this is an error one must be noted eitheri n the local server log or Zenphoto's own. Otherwise it will be impossible to find out. If you tried to sort one album with lots of images and also subalbums with lots of images you might have ran into a server limitation. I don't know which one though. Maybe my colleague later will have an idea.

Did you happen to try a database refresh before you emptied the tables? Perhaps there were some problems in the database. The refresh will usually clean those out.