I'm having the same issue with Lightbox 2....
I was using Lightbox 2 with WordPress before the upgrade, and it worked perfectly! After upgrading to WP 2.7, the Lightbox does not work with any new images, but is continuing to work with images added prior to upgrading.
I deactivated the Lightbox, deleted it from the directory, and installed it freshly (Lightbox version 2.8.0)--but still have the same problem (still works with the previously added images, just not with any images added after the upgrade).
I tried installing Shadowbox JS, but it behaves similarly--works with images added prior to upgrading to WP 2.7, but none added after upgrade.
Any suggestions?? Thanks!!!