Text is blank in Messages

For some reason the text and graphics are blank in my messages (either in the reading pane or when I open a message). Any help would be greatly appreciated.

What version do you have? Have you upgraded recently?

It appears that I have version 4.0. I don’t remember updating, but I thought I was on version 3.0 before. Maybe there is an auto update feature?

Send me one of the problematic messages saved in .eml format. Simply right click on it and choose Save as. Thank you.