[imp] PGP-encrypt message could not be decrypted in OE

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Hi there:
I use Horde head+IMP 4.0 and send pgp-encrypt message successfuly to another
user A ,who use Outlook EXpress +PGP plugin as MUA .

My problem is ,user A complain to me that his OE+pgp plugin could not decrypt my
pgp-encrypt message.Here is the OE message view for that mail from user A
http://210.241.49.67/~txg16/tmp/oe.gif

and here is the error message while click on "decrypt current window" in OE
http://210.241.49.67/~txg16/tmp/decrypt_err.gif

Note:User A have tried two OE plugins(product of WinPT.org and pgpi.com) and
both of them got the same problem.Is this is IMP or OE plugin problem ?

David