A new page type is available on our production environment, but when I click the new page type, set a title and click 'OK', I get an error message saying 

Unable to load /EPiServer/cms/Stores/contentdata/
status: 406

I can create other page types within the same structure. 
The new page type does not have any required fields; I've also tried to do 'Revert to Default' for this page type (allthough it's completely new and nothing has been changed outside the code) and then I get an exception as well. I have no access to the production logs at the moment, will update this issue as soon as I know what the error is...

I've also tried just adding a field through Admin mode, but get the following error:

The INSERT statement conflicted with the FOREIGN KEY constraint "FK_tblPropertyDefinition_tblContentType". The conflict occurred in database "nuonnl-sqldb-prd", table "dbo.tblContentType", column 'pkID'.

Any ideas why this is happening to our new page type?

UPDATE:
A restart of the application fixed this error, but I still think this is a major issue which should be looked into