gpg4win-2.0.4's problem on windows XP

Before installing gpg4win-2.0.4,I use another way to encrypt/decrypt e-mail,it should be S/MIME.
But,today,after installing gpg4win 2.0.4.I found a problem at opening former encrypted email,although I can successfully encrypt/decrypt mail using gpg4win.
The total error message is :
“The GPGME library returned an unexpected error.The error was: No secret key. This is probably a bug in GPA.GPA will now try to recover from this error.”
I’m not sure if it’s really a bug.But,I need to use gpg4win for job, and I also need to read former encrypted mail for reference.
Can anyone support me to resolve it?