[QA][4.7] Why does the gpg command report an error message when it attempts to decrypt encrypted data?

Issue

• When our customer encrypted a file by the gpg command of gnupg-1.2.6-9, they encountered the problem described in BZ#510500.
• They updated the gnupg package to gnupg-1.2.6-9.el4_8.1 to resolve the problem.  When they attempted to decrypt the file encrypted by gnupg-1.2.6-9 by running the gpg command in gnupg-1.2.6-9.el4_8.1, the command aborted with the following error message.

gpg: [don't know]: invalid packet (ctb=2d)