Following on my posting below where I was unable to add a second user, I am now trying to reconstitute this zenphoto installation with a new installation (which can - I have checked - add a second, third, fourth or whatever user) but with the old albums and database.
I tried following your restore instructions to a certain extent.
I uploaded the current version 1.5.7 -
I copied into this location the existing album folder with its contents
I copied the cache and the cache-html
I copied the backup folder with the database backup
I ran setup - specified a new database - I was given the opportunity to restore
When I clicked on the restore link the process started but all I got was a blank screen.
When I checked the debug log it contained the error below (a second attempt as above produced the same error message)

Any help would be appreciated.

Thank you,
Richard

{19587:Wed, 06 Jan 2021 14:05:57 GMT}
USER ERROR: MySQLi Error: ( SHOW INDEX FROM `[DB]`.[name_of_folder]_admin_to_object ) failed. MySQLi returned the error You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '-new_admin_to_object' at line 1 in /home/folder/folder/folder/zp-core/functions-db-MySQLi.php on line 95
trigger_error called from query (functions-db-MySQLi.php [95])
from query_full_array (functions-db-MySQLi.php [130])
from db_show (functions-db-MySQLi.php [327])
from backup_restore.php [288]

OK - sorry to bother you - though it would still be useful to know how one can restore when one has the database and the album folder.
The problem with the second User was solved by setting massive amounts for upload_max_filesize, post_max_size and memory_limit in php.ini file.
Should have tried that sooner, of course!
Thanks,
Richard

The error suggests that the table prefix used in the database is not set correct on the site you tried to import so it failed. The prefix is part of the table name so the table failed.

You were basically moving an install. We have detailed info in moving:
https://www.zenphoto.org/news/installation-and-upgrading/#--moving-existing-installations

respectivly the main article:
https://www.zenphoto.org/news/moving-and-changing-existing-installations/