GPGOL tries to be compatible with PGP Desktop. It uses the PGPExch.htm file,
that the PGP Desktop Client knows, to show the formated content from this
attachment.
However, GPGOL makes 2 mistakes - making it unable to work:
GPGOL created a detached signature for this format i.e. it creates
PGPExch.htm
PGPExch.htm.asc (the detached signature)
PGP Desktop and other applications cannot cope with this, they only expect one
file - PGPExch.htm.asc. What happends is, for example in PGP 8.0 - that a dialog
popups with an internal error because it does not expect a detached signature.
This error alone would not cause the issue, there is another issue - you are
using *.asc extension for a DETACHED signature. All clients only use *.sig
binary encoded detached signatures, never armored ascii detached signatures.
Please review how to implement the pgp partioned format correctly here: