@craigwarren85 I experienced the same problem recently when i migrated from Windows 7 to 10. The Recalbox/share folder was not listed on the devices. My solution was; In addition to the solutions above, make sure that Recalbox is connected to the network. Open the Network menu on the EmulationStation and see if "Connected" appears. Copy the IP number. Go to Windows, open My Computer, on the left side select Network. It will display on the right side a list of the devices connected to the network. If Recalbox does not appear, click on the address bar at the top of the window and type "\IP number" (Two bars \ before the IP number. For some reason when i put two bars here it only one appears after posting) IP number that you copied from Recalbox and press "Enter" on the keyboard. In this way, Windows accesses Recalbox and displays the "Share" folder on the screen. You can try to disable the anti-virus/firewall. They may be preventing access to Recalbox. Remember that each time you connect Recalbox to the network, the IP number changes, but there are usually few variations and only in the last digits.
Sorry if my explanation has become inconsistent somewhere. I don't speak English and i'm using the Google translator.