decrypt failed - secret key unavailable

[davidemelan at tin.it]

Sorry, this probably a FAQ but I didn't find an answer and I need help.
Soon.

I rightly imported two public keys, both ELG-E 2048 bits, one from PGP 7
and one from PGP 8.

I'm able to crypt messages to those recipients and they can decode and read
my mails, but when they answer me, trying to decrypt messages I get the
error message as in the subject.

Could someone help me?

Thanx in advance.
davide.