Problem with a backup to a server with backup utility

I'm doing the daily backup of a server in a hard drive that have network but when I do it displays the following message: 

The backup file name Could not be used 

"\\ Dunnas001 \ backup \ SDUN001 \ New \ DISCO_E_DIARIO_211014.bkf" 

Please Ensure it is a valid path, and That You have Sufficient access