Anyone any ideas why I can't create models in the backoffice - running VS Studio and trying to click the Generate Models button and get the attached error.

@Owain did you find the culprit? I notice the exception happens in Contentment as part of the data list value converter. I don't think it's because a block item is null, but the error on your last screenshot does make sense if an element type has been deleted, but a block item still references that element type (the error on the last screenshot) and the Contentment data list - possibly via a custom data list source - references the deleted element type.

Ye. I think it was this and also I was working on a new branch that didn't have my original changes in it so maybe a bit of that too causing the issues