Columns on the Entry index page giving errors For some reason whenever I add a custom column to a section's entry list I'm getting errors and no values.

If I add Entry Type to the column list, for example, it's saying:

Unknown class: Craft\EntryTypeModel


And links are saying:

Unknown class: Twig_Markup




I'm a little dumbfounded?  I tried removing and re-adding them and still no luck.  Any ideas?
So turns out it was an issue with an older plugin, DashCols. As soon as I disabled it things worked fine.  

Unsurprising in hindsight!