Sync error on sync to local sync store

Running DTP Office 2.8.7 on OS X 10.11.1

I am syncing a database to a local sync store (located on a NAS device). This I have been doing for sometime without problem.

Now I am getting the following error message:

Once this occurs it is no longer possible to synchronise until DTP Office is closed and re-opened.

I do not understand the message as the file indicated in the message is not of the type that would be in the database.

What do I need to do to solve this problem?

Please start a Support Ticket.