Are you using Win10? If so, I find it can be picky about shared directories (not like the glad hand of XP), though I have used PCMANFM with Lubuntu, even as old as 10.04, and swapped files with Win8.1.
If you haven't already tried it, perhaps disable all passwords of Win public folders, Win firewalls, etc to see if it's a Win issue.
Also, have you tried making a Public folder in Debian to see if Win10 can find it?
Jake