OE6 asking me to define.....

Everytime I am trying to sent an email, OE6 asking me to define if I want to send my message:
Send HTML
Send Plain Text
Cancel (return to editing message)

I checked Tools/Options/Send and mail sending Format HTML is ticked.

Can anyone tell me why has this behaviour started out of no where? I downloaded the latest IE6 Critical update lastnight.

Thank you.

Sorry to trouble you but I have just found out why......In my address book each entry has "send plain text only" boxed checked (I have no idea why) so I have to uncheck each box to get rid of this irritating message.