I am having the same problem. Zenphoto has changed the URL parameter syntax in this (or some recent) version. That means zenphotopress must be updated too!
I see the plugin hasn't been updated for quite some time, is it still alive?
Even if the author does update the plugin, all images already in wordpress blog posts will have to be updated (as i believe the plugin just writes the image url into the post)!
If we can find out what the new URL parameter syntax is (zenphoto forums), then the easiest way would be export the wordpress post database table, open the sql file in a editor (like textwrangler) and use the search and replace feature to replace all wrong urls with the right one. Save, then import the database table back into the wordpress database. (you could also do this with SQL statements, but is tricky if you're not fluent in SQL).
My example is:
WordPress blog post: http://www.exploringbliss.com/2009/08/into-the-wild/
Broken image url: http://www.exploringbliss.com/photography/zp-core/i.php?a=canada&i=20090826-Canada-2701.jpg&w=590&h= (note, by removing the parameters "&w=590&h=" , the image will load in full size)
Zenphto page: http://www.exploringbliss.com/photography/canada/20090826-Canada-2701.jpg.php (note, the link here still works from the wordpress post)