Sorry, I was on the computer, but I wasn't checking TWG.
IRQ is a hardware error. It means two or more devices are trying to use the same IRQ port at the same time. For this to happen when you aren't making any changes to the hardware, however, indicates that something very odd is going on.
You say after restoring to an earlier point, you're not experiencing the problem, though, so it likely indicates that the Operating System is the problem spot. Although it still might be that a piece of hardware is failing.
Let me try to narrow it down. what were you doing immediately before the error came up? something that was happening must have made the change (note: this doesn't mean you were doing anything wrong, but it helps me pinpoint the causality).
Try importing your mail to Outlook Express and see if you can operate normally. Make changes one step at a time so we can see the effect of those changes. If the error occurs again, we can see what may be causing it. (and if it doesn't happen again, then we won't worry about it)