When trying to upload documents, if a System.NullReferenceException Error appears, check the “More Details" button, if the error is occuring from a UploadManager() object, use this fix.
This error occurs when documents are in a state of Uploading, but the Upload Status is set to Idle when checking using the Edit->Upload Status option.
Go to My Documents->FileDirector->XXX.CAB and edit the “DocManager.xml"
Do a replace in NotePad or whatever you are using, to replace
Open the cabinet in FileDirector, all the local documents should be showing checked out, and can be re-checked in.