- Go to the menu OpenPGP > Preferences
- In the section Files and Directories, activate the checkbox "Override with" (Enigmail v0.95.x only)
- Enter the following path: C:\Program Files\GNU\GnuPG\gpg.exe
Note: The problem is that gpg4win creates a wrong entry in the Windows PATH environment variable. Alternatively, instead of the workaround above, it is also possible to change the PATH such that "\pub" is removed from C:\Program Files\GNU\GnuPG\pub.