Any reason I would get the error below when I click the edit button on the theme selection page? Happens on zpBootstrap & zpArdoise.

Cannot edit this file!
Fatal error: Cannot edit this file! in /home/content/55/2392255/html/gallery/zp-core/functions-common.php on line 294

Any other errors in the server logs ?

Most likely it's the file/folder permissions.
Please see: http://www.zenphoto.org/news/permissions-for-zenphoto-files-and-folders

It may also be strict server security settings. That is something you would have to ask your host about.

hi
in fact, this issue occurs for every 3rd party themes.
when I try to edit a theme, I have this message : Cannot edit this file!

Never had this locally.
For some live sites I had to ask the host to lift security restrictions on certain folders/files.