Not the most active community I have seen:-( for anyone else having the problem what did in the end, was disable and then uninstall the device from the machine, restart, it automatically re-installed the device and for now seems to work - odd but true, Peter. 
Hi, I have an XPS 13 running windows 8.1 Professional, Windows Update fully up to date, Dell Support Assist fully up to date too!  When I access my local \\diskstation via a USB/wired link everything is fine, when I disconnect and use wireless I get the error "Windows Cannot Access" the diskstation.  It is connected to the wireless network and has access to the Internet and other services - just refuses to see the diskstation  I have two other Dell 15" laptops running 8.1 Pro in the house that access the diskstation wirelessly no problem...  so I am wondering if there is something odd with my Intel AC 7260 card or config?  Any suggestions appreciated!  Peter
XPS13 with Intel AC 7260 "Windows Cannot Access" local disk station