It's a real PITA to fix, but this will do the trick; (LC - left click, RC - right click)
RC Wi-fi symbol on the status bar and LC "open Network ...."
LC "Change adapter options"
RC the connected Wi-fi
LC "Properties"
LC "Configure"
LC "Advanced"
LC "Band" and from the drop-down on the right LC either 2.4 or 5 (De-select "Auto") depending on what your router does.
LC "OK" and close the various dialogues.
RC the Windows start button
LC "Device Manager"
Open the "Network Adapters" collection
RC the Marvall Wireless adapter
LC "Uninstall device" (I know, I know)
DO NOT DELETE THE DEVICE - Just uninstall it.
Restart your SB
The driver will magically reinstall upon reboot and all will be well.