It was happening like that to 2 friends of mine today ( who called me to asked if something is wrong with their PC that caused it) almost the whole day. Not sure if it is rectify yet but I have no problem with mine. I think it is happening to certain email accounts and maybe it is dependent on the server that holds it.
yah... it happened to me on my laptop with IE7 also for a certain period of time and it works fine with FF.
on IE7, the bottom left corner will show the error sign.
can click to "open" the email but nothing happens
but now ok liao.
dunno if it's my laptop cleanup or not