Britgirl, thank you very much (and sorry I just saw your response – I had given up on solving this!).
Is there any kind of work-around if I’m willing to take drastic measures – for example, completely uninstalling Avast and using a different antivirus? That is indeed the one I’m using, so that’s the bug I’ve run into!
I did do that, and I’m also going to try using an ethernet cable on the Windows machine (right now it’s a wireless dongle) and “restarting” the Mac (which I didn’t think was necessary). But neither of those seem to make sense since I can see the Mac with my Windows PC and control it… just not the other way!
Any help would be really appreciated, I’m stumped =/