I have upgraded to zenphop 1.5.6 by coping the index.php, /themes and /zp-core files/folders as the update help tells me but the install routine says the zenphoto.cfg.php file [does not exist] but I am looking at it right now. what could be the problem.

what logs or more info can I give you for help

Ubuntu 18.04

Thanks for your help

If you upgraded an existing install that is still within the zp-data folder.If you deleted that folder, you need to re-create it (or upload it) and let Setup create a new config file.
Otherwise why an existing is not seen I cannot tell. Please review your error logs.

I didn't bother zp-data since the upgrade instruction did not say anything about that

upload the new files :
index.php
/themes (or actually just the four official themes within - again backup if you have custom or customized themes within this folder!)
/zp-core (especially here make sure that really the entire content is replaced so that no orphaned files because of removed or renamed ones are kept)

Where are the error logs and what are they called
Keith

Found the issue, the permissions on the zp-data folder were wrong

didn't bother zp-data since the upgrade instruction did not say anything about that

Well it says:

Download the latest version and upload the following files and folders. Since FTP clients tend to mess overwriting, especially folders with lots of files, best practice is to delete the old files first and then upload the new files :

Then the list which is referred to follows. It does not really tell to delete everything, just the old files of those you upload. You don't delete your albums folder either as you would loose all of course gallery content…

Zenphoto's error (debug) log is within zp-data as well. Where your server PHP error log only your host can tell you.

Found the issue, the permissions on the zp-data folder were wrong

Glad you found it. This somehow happens on some servers somehow sometimes…