Agent failed to get password from pinentry-gtk-2

[XeCycle]

Hello, I added gpg-agent to my .profile recently, but I cannot
use it now.  By some debugging I found it failed to get the
entered password from pinentry-gtk-2; with pinentry-curses it
works.  pinentry-qt4 is even worse, it complained about "no
pinentry", though I have it installed and is sure I have the path
right.

What can I do in this case?  I use gpg mainly from Emacs so I
don't think I'll be able to use pinentry-curses all the way.

Here's the versions I use:

gpg-agent (GnuPG) 2.0.18
libgcrypt 1.5.0
Copyright (C) 2011 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

pinentry-gtk2 0.8.1

gpg (GnuPG) 2.0.18
libgcrypt 1.5.0
Copyright (C) 2011 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Home: ~/.gnupg
Supported algorithms:
Pubkey: RSA, ELG, DSA
Cipher: 3DES, CAST5, BLOWFISH, AES, AES192, AES256, TWOFISH, CAMELLIA128, 
        CAMELLIA192, CAMELLIA256
Hash: MD5, SHA1, RIPEMD160, SHA256, SHA384, SHA512, SHA224
Compression: Uncompressed, ZIP, ZLIB, BZIP2

Thanks for any help.

-- 
Carl Lei (XeCycle)
Department of Physics, Shanghai Jiao Tong University
OpenPGP public key: 7795E591
Fingerprint: 1FB6 7F1F D45D F681 C845 27F7 8D71 8EC4 7795 E591