I installed cygwin on a 'new' machine (well, a fresh disk, after Encryption Anywhere made my old one unsalvagable). After the install (and a reboot, I believe) a new bash window gave me this message:
cygwin mkdir: cannot create directory `/cygdrive/m': No such file or directory
where M: is the (network) path to my home directory (aka %HOMEDRIVE% in windows). M: was available, but I couldn't get to it from cygwin. Also, I couldn't manually mount it.
After doing some research, I didn't find a solution. People who weren't logged in to their domain at the time seemed to have the problem occasionally, but I was logged in. Maybe rebuilding the passwd/group files? It wasn't affecting me at the time; I had other things to do, so I put it on hold.
At some point, I rebooted, and the problem was fixed... kind of annoying for a problem to fix itself like that, but that's Windows for you--good enough that you sometimes forget it's a substandard operation system.
Maybe this will help someone else from wasting time on a problem that might be fixed by rebooting Microsoft Windows. Remember when you had to reboot after any change?