I *THINK* I have narrowed this down to a conflict with another running app. I've had this problem for a few months and it occurs generally once a week.
Last time it happened I killed several background apps and it fixed the problem. Next time I will try to narrow it down.
In the mean time let's see if any of you are also running one of these apps so we can see if there's a correlation.
The apps I killed were:
32bit Fax
Outlook 2003
WinPatrol
Logmein
PopPeeper
AnyDVD
Google Calendar Sync
Faststone Capture
Display Fusion
Allway Sync
Eraser
TaskIcon
Hott Notes
My prime suspect would be Faststone Capture. This is a screen capture app that intercepts the PrintScreen key, probably in a similar manner that Macro Express hooks into the keyboard. Runner up would be Hott Notes (a Post It note program) which also intercepts the keyboard for hot keys. I happen to have hot keys disabled in Hott Notes since I don't use them, but it's possible that there is still a conflict involving the hook into the keyboard. None of the other apps would seem to have anything in common with the way Macro Express functions.