Thunderbird: Enigmail PGP Problem

Recently I started using the Enigmail extension for Thunderbird which uses GnuPG to encrpyt or sign e-mails. However, there is a strange error that sometimes occurs when recieving PGP encrypted e-mail or trying to import public PGP keys from an e-mail. The e-mail refuses to be decrypted manually or automatically and comes up with the error "Error - No valid armored OpenPGP data block found". Strangely the e-mail is magically decrypted when one hits the reply button. The problem seems to happen to a lot of people and there isn't much clue online as to a solution. However, I discovered that the problem lies in the fact that PGP does not like to deal with any HTML in e-mails. Simply select: "View" - "Message Body As" - "Plain Text" and the problem is fixed.