My Windows 7 PC has been reading both PCM and SP discs transferring the files from my Sony RH1, together with MD discs recorded on my MZ-90.
When connecting my RH1 containing an MD recorded disc yesterday, a box appeared in Sonic Stage inviting me to download an updated driver, which I did. After that My PC was not reading MD discs.
I have now reread all of this thread and was able to reinstall the netMD760 driver - all is now well! The trick is to look at "Other Devices". in Device Manager for the yellow exclamation mark icon, right click that and then "update driver" which it will find on your PC. Once installed, NetMD will appear in USB Controllers and disappear from "Other Devices".
Presumably the netMD760 driver became corrupted on my PC.