problems with mailcrypt and XEmacs 21.4.13, VM 6.92

[Julian B. <jc...@in...>]

I'm finding it impossible to get mailcrypt (3.5.8) to work with vm,
and wonder if anybody can point to me the right FAQ...

My base system is VM 6.92, XEmacs 21.4.13, but I've also tried it
with a clean build of XEmacs 21.5.16 with VM 7.17.

I use gpg, so I set  mc-default-scheme to "gpg".
Then when I do mc-decrypt from my VM summary buffer, I just get
"decryption failed: gpg", with no other information anywhere that I
can find.
(From the command line, gpg deals with the message quite happily.)