Featured Image in 3.0 after upgrade

Hello everyone.

I have been happily using WordPress since 2.4. I upgraded to version 3.0 the other day and so far things have been going wonderfully. Until I realised that the Featured Image thing isn’t working.

I have added all the relevant code to my functions.php and index.php page. I then go to assigned a picture to my post. I select a thumbnail, click Set as featured image, then Save. There is some loading, then “-1” appears in the Featured Image box.

I was convinced that I was doing something wrong, until I went to a different website with a fresh 3.0 [not upgraded] install and it worked as it should have.

Has anyone else experienced something like this? Does anyone have any suggestions? Thanks