I get this message:
"Outlook Express encountered an unexpected problem while displaying this message. Check your computer for low memory or low disk space and try again." when trying to open a message. But I know I am NOT low on disk space or virtual memory?, any idea?
512RAM, and when I look in the Task Manager, only half of my RAM is being used at the time of the error.

Sorry, but I'm not really sure. I'm guessing that the RAM allotted for Express isn't enough, and that you need to boost it. But if you have an account an Answers, then you should have one on Mail, so it's beyond me why you're using Express. The formatting is weak and to be brief, well, it sucks.

At that instance, the message required more RAM to display. You may consider upgrade your RAM (increase) to bigger capacity. What is your current RAM size? What is your operating system? What are the programs that you are running are all related?