When using Emacs 24.3.1 on Windows 7, I found that cygwin-mount.el would not work (it gave a bogus error of being unable to locate mount.exe) or using version control (cvs) within Emacs would fail with “Permission Denied”. Turns out the problem was Windows UAC (User Access Control). By changing the properties on runemacs.exe to “Run as administrator”, I was able to fix this issue.