I cannot understand why, but, I did a fresh installation in another folder on the same web server and it works fine.
So, basically, I would say that the issue is not related to the host (it didn't change) and not related to my local browser or something else (it didn't change too).

The issue could only be on zenphoto side. Something was going wrong, but what...

Have you re-installed zenphoto on the site that fails? If so, then it cannot be related to zenphoto either!

So if it's not the host, not ZP and not local, it's a ghost ?

The only thing I changed : new ZP installation in a new folder with a new DB on the same host with the same client.

So the new installation works (as the old one for few months). It cannot be related to the host or to the client.

album password not working please help me

sudhirsingh, please open a new topic (this is not about your problem) and add some details (if you are serious...