Troubleshooting ImageFile upload Failed

I am in need of some smarter brains to help me troubleshoot an issue with an ImageFile upload. I set up an "ImageFile" type, inheriting from ImageData, to be able to add image files to Episerver. The implementation is pretty straight forward:

	[ContentType(DisplayName = "ImageFile", GUID = "4a31542c-b536-47a9-a1f0-9e1e236a06de", Description = "")]
	[MediaDescriptor(ExtensionString = "jpg,jpeg,jpe,ico,gif,bmp,png")]
	public class ImageFile : ImageData {
		public virtual string Copyright { get; set; }
		[Required]
		public virtual string AltText { get; set; }
	}

To upload an image I open the content sidebar, navigate to the Media tab, select a folder, and press + icon to add a new one. When I select an image to upload and hit okay, it goes through the upload process, shows the status bar, and then shows a "Failed" status. Interestingly, the content sidebar refreshes and shows the image, and the log files in App_Data don't show any updates or messages related.

Does anyone have any ideas on this? What can I check? What can I look for?

Thanks.