I'm currently running 1.5.7 on a live site without any problem. I also have a development version of the site which I use to test any updates before going live.

I've been trying (intermittently) for weeks to update - first to 1.5.8 then to 1.5.9 but I'm encountering difficulties.

To try to resolve the problems I wiped all files from the development version and reloaded 1.5.7. However when trying to install I get many entries like the following in the Debug log:

NOTICE: Undefined index: CHMOD in /home/bpskdk/public_html/development/zenphoto/zp-core/functions-basic.php(127) : eval()'d code on line 82
eval called from require_once (functions-basic.php [127])
from require_once (admin-globals.php [12])

followed by different filenames such as
from admin.php [11]
from admin-logs.php [8]
etc

All the errors relate to Undefined index: CHMOD

I have checked file paths and don't see anything wrong but I'm no server expert.

Other attempts to update to 1.5.8 and 1.5.9 on the development site give similar error messages, with the screen often going blank and freezing.

Installation information from my last attempt to go back to 1.5.7 (which appeared to have succeeded apart from the debug log entries above):

Zenphoto version 1.5.7 (Official build)
Server path: /home/xxxxx/public_html/development/zenphoto

WEB path: /zenphoto
PHP version: 7.4.25
MySQLi version: 8.0.27

Any help would be gratefully received.

NOTICE: Undefined index: CHMOD in /home/bpskdk/public_html> /development/zenphoto/zp-core/functions-basic.php(127) : eval()'d code on line 82
eval called from require_once (functions-basic.php [127])
from require_once (admin-globals.php [12])

That indicates a possible problem with your config file as that is one line that loads it via eval()up to 1.5.9. In the coming 1.6a it will not use eval anymore.

Do you perhaps have a typo somewhere in your config file?

Actually there is no index CHMOD in the config file, the uppercase writing indicates a constant but we actually have only the constant CHMOD_VALUE. "chmod" otherwise is of course a native PHP function.

My sincere apologies for the delay but have just got round to completing the update to 1.5.9
The problem as noted above WAS the config file. I'd been keeping the same file through all updates but once I deleted it and allowed it to be recreated it fixed the problem.
Thank you.

Thanks for the follow up! Glad it is solved!