I had a few reports of that and it turned out the machines had either an infection or an incompatible set of protection.
One person had installed more than one antivirus and the other had a trojan on the PC.
I've yet to see this as an issue with WLM and 7 alone.
I am using Windows Live Mail and Widows 7. Live Mail works very well except for an error message 'A problem occurred while trying to open this mail. Please try again' This message appears when opening nearly all messages the first time but seldom when reopening them. With one addressee it never comes up. Trying again does not solve it. Greatful ffor advice on how to cure this irritaating litle problem. Thank you.