Media uploader size options not selectable

Hi, I’m administering 13 very similar WordPress blogs at work, they all run as sublogs in WordPress MU 2.9.2. I have googled and read through this forum for answers, but still can’t seem to solve it.

I have set the sizes in Settings->Media, and the Large is set to my theme’s max width (currently 460). When uploading a new image, the radio buttons Thumbnail, Medium and Size are not selectable at all, only Full size. I’ve tried small and large images (from 20px to ~2000 wide), different images, different imagetypes (jpg and png, none are grayscale), but the radio buttons just never become enabled.

I’ve tried setting $GLOBALS[‘content_width’] = 460 in my theme’s functions.php, no difference. I’ve tried disabling all plugins, no difference. I’ve tried to change the theme (even WordPress’ default theme), it’s the same with them all.

The users of the blogs are as far from code monkeys you can go and are having a hard time understanding the following directions: Upload, and insert an image. Then click on the image in the post editor, click the “mountain” icon to edit it, then choose a percentage, preview the post and adjust. I just want the “Large” option to be enabled, that would solve everything.

We’re considering upgrading into WordPress into 3.x, but it’s on hold because of the number of blogs running and the risk of something going wrong. I run WordPress 3.0.1 locally and when using the same plugins, theme and settings, the radio buttons are always enabled with the correct sizes!

Is this a bug in MU 2.9.2? Any ideas how I can solve this? I’d appreciate any help!