When installing GPG4Win 1.0.1 on a different partition (i.e "D:" instead of "C:"), WinPT could not identify gpg.exe although the default “%ProgramFiles%” directory is set to "D:\Program Files" in the registry.
I resolved the issue by installing the thing on “C”. This may not seem much to many, but it is a pain in the neck to have to do something twice.