Trouble moving files to network drive

[351Windsor]

I was hoping someone could help me with this, what I have is a newer mac mini connected to a netgear wndr3700 router via ethernet port, and a W/D 1TB my book for mac external hd connected to the router by usb. I can access the hard drive no problems, but it will not let me move files to it. I'm logged in to the mac as an administrator, and into the router as administrator. it asks for password to move files, i enter it and it comes up with the message i've attached. Thanks

 

[Lokrado]

change the permissions on the items you want to copy, and the disk

the easiest would be just to make it all everyone - read/write
then apply to enclosing items