[Plugin: File Gallery] Custom Fields in version 1.7.4.1

Hi,
The plugin is great but I wanted to set a different thumbnail image for each of my pdf files. I found no direct way to do it so I thought about creating a custom field for each file containing the link to its specific thumbnail.

I am working on a page (not a post). After I add the custom field the page gets refreshed and directed back to the posts list. No custom field was added.

Any idea?

http://wordpress.org/extend/plugins/file-gallery/