I have a custom document library and a custom document set content type. When I add a document set of that type to a library, I am immediately taken to a screen saying that the URL for the new document set is invalid. The message is as follows:
The URL [url here] is invalid. It may refer to a nonexistent file or folder, or refer to a valid file or folder that is not in the current Web.
The document set does get created, though. And the URl from the error message is valid (which makes me wonder whether Sharepoint is trying to access it before it is created). If I create it via browser, then it is created just fine, but if I create it through a workflow, then it is corrupted from the start - they show up in the library but their welcome pages throw errors of the 404 kind.
Now the most interesting thing: It doesn't matter how I create the library and the content type. If I do it in Sharepoint Designer, Visual Studio, or directly through the browser - in all these cases, I get the same problem. And only with custom document set content types.
It only happens in 2013, be it a purely Sharepoint Online hosted solution, or an in-premises hosted one (I have access to both kinds of environment here). It also does't matter whether the site collection is using the 2010 or 2013 user experience model. In a pure 2010 environment, though, everything works fine.
I have tried provisioning them with default documents, and many combinations of settings, and I'm still getting this error.
Since the error page shows a correlation ID, I have also lurked through the ULS logs trying to find out what's happening. I just can't find any errors there, other than the system trying to find a non-existing URL.
Has anybody been through this? Can someone help this poor soul defeat this dragon of a problem?