Once you enable Collabspaces in NetDocuments there are several restrictions of NetDocuments functionality as a result.

If you are enabling Collabspaces you will get this warning about the impacts on that cabinet

The main one that seems to have impact on our customlers is the 2nd bullet point in the above image. 

That details that you are unable to use External Users in the same way that you have done previously and can not grant external users access to NEW content expect via a Collabspace.  ie All content must be shared in a Collabspace only once Collabspaces are enabled.

All existing content shared via External users will remain and continue to work but you can not add add new permissions to new items.

You can review more information about this via the online user guide of NetDocuments Click Here

Here is the section that describes this limitation