Mail has stopped displaying HTML messages. Why?

[rjmusto]

I am running 10.6.8

For some reason I can not fathom, Mail has stopped displaying the content of emails with HTML formatting. All I get is:

To view the message, please use an HTML compatible email viewer!


It used to work fine, so what has happened? I've checked the Preferences to make sure HTML is enabled.

Thanks.

 

[MisterMe]

Do your old HTML messages no longer display properly or is this a problem only with new messages?

 

[rjmusto]

Just checked and the old ones do not display either.