[Enigmail] Unverified signature error

[David]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

What, exactly, does this mean? And why can I not verify this signature?

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OpenPGP Security Info

Unverified signature

gpg command line and output:
C:\Program Files (x86)\GNU\GnuPG\gpg.exe
gpg: Signature made 07/14/09 17:50:26 using RSA key ID 1C109517
gpg: WARNING: signature digest conflict in message
gpg: Can't check signature: general error
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- -- 


  David
-----BEGIN PGP SIGNATURE-----
Comment: --batch

iEYEARECAAYFAkpd5UEACgkQzrAMrEP3F1qzwgCeJdkBrgTPSAhFyDpFPJQfpbf2
DfYAn0mNKEGfDTO+/93Vx9MHxPX9srD+
=8bFK
-----END PGP SIGNATURE-----