I just recently bumped in into this thing – you have to enable Document Sets on a library level before you can actually use it. This little point baffled me a bit when I tried to use Create Document Set SmartWizard in K2 Studio:
It took me a while to switch over too my SharePoint document library to realize that I just can’t create document set there:
Normally the same New Document menu contains an option to create Document Set. Well now it’s clear that “Required field is empty” error is just a clumsy way employed by K2 Studio to tell you that Document Sets disabled for your library.
To enable them you just go to Library Settings > Advanced Settings > Allow management of content types as on screenshots below.
Click on Library Settings button on ribbon:
Click on Advanced Settings:
In advanced settings select Yes for Allow management of content types and hit OK:
Now you also need add Document Set content type using Add from existing site content types link in library settings:
At this point you should be able create document sets in SharePoint just fine:
Yet you still going to have problem with K2 SmarWizard I mentioned initially. Why? Just go to K2 App settings for your library to see the answer:
Just click on Regenerate SmartObjects, go back to K2 Studio and Create Document Set SmartWizard to see things working there:
Voila, we can now see our Document Set enabled library and use SmartWizard to create document sets in it.
Just to recap: To be able to create document sets within SharePoint libraries you have to Allow management of content types in Advanced Settings of this library and add Document Site content type using “Add from existing site content types” link in library settings.