Error in eB 15.6 'The Id is < 1. Use the overload to pass the Id'


We have an install of eB 15.6 which is returning an error when trying to update the Default Navigator, but we're not sure what the error is trying to tell us. We get this error for all users, including the Admin account. On a different community, set up similarly, the functionality works but not sure where to investigate if the Admin account won't apply the update.

Any help much appreciated - many thanks,