While doing an upgrade of a large database to NAV2013R2 we are sometimes getting this message when trying to change a tabledefinition.
The reason we are getting this message is the new way the metadata changes are synchronised as documented in the NAV Team Blog here.
In earlier versions of NAV when you did a change on a large table in NAV, the Object Designer would wait until the change was done on the SQL Database until you could continue working. NAV2013R2 gives you control back immediately, but you cannot do anything until the change is finished at the backend.
Anoying, yes, most definately.