Is it possible to use an external folder for images? Or not.

It s possible, with limitations. You must modify your zenphoto.cfg file to point to the folder. The comments in the file explain how and tell you of the limitations.

Yes, but it says:
{
$conf['album_folder'] = '/mnt/32g/albums'
$conf['album_folder_class']= 'external'
}

"Fatal error: Error: The 'albums' directory (/mnt/32g/albums/) cannot be found. in /var/www/clients/client0/web2/web/album/zp-core/functions-common.php on line 280"

IF you mean by "external" on a different server, no. If you mean you can rename it or have it above the webroot, yes. FOr the latter use relative paths (../.../albums).

It is on the same server in the "/mnt/32g/albums/" directory. The Zenphoto itself is in the "/var/www/...." directory.

The comment says:

// 'external' -- the folder must be a [b]full server path[/b] to the album folder.
// Images within an external folder are not visible to web
// browsers, so certain features such as flash players cannot
// display them

You have not done that. I can only guess where that folder is supposed to be since it is "external" but I would guess you have left some portion of `/var/www/clients/client0/web2/` from the path.

Forget my comment about the relative path....should read our own docs....

The full path to the new album is "/mnt/32g/albums".

Well, the you have a problem because the error you got says that folder cannot be found.

"Fatal error: Error: The 'albums' directory (/mnt/32g/albums/) cannot be found. in /var/www/clients/client0/web2/web/album/zp-core/functions-common.php on line 280"

This error is from your server, not Zenphoto, so your server does not believe you.

I will see the solution on my server. Perhaps I find it.