Hi this is specifically for Uncle Cheese as I didn't know how to get a hold of him. Hopefully this gets to you...
Seems that 2.4a dropped the Image_Uploader class. It would be nice if more of the deprecated classes and methods are tagged as such before they are removed but hey things change... anyways, here is some details on where the class was and what issues it caused when I upgraded.
Let me know if you need a hand with it.