The first thing I would do it check the database table dbo.lists,

USE YourDataBaseName
SELECT distinct listName
  FROM Lists

 To make sure that you have the category in your  table and make sure your table has not somehow become corrupted.

 Then

SELECT *
  FROM [dnndev.me].[dbo].[Lists]
  where ListName = 'ImageTypes'

To see the details of that category

If the table spits out the full category list, I would suspect a problem with the lists module