Kevin,
A quick look at my C:\Windows\System32\ folder I only found a "mstask.dll". I have no clue what the mstask.exe file could be. It might be you DLL file renamed but to be on the safe side I would rename it to "mstask.old" and a quick search of my windows xp pro cd I found the mstask.dll file. Might be as simple as copying that file back to the path and rebooting.
If that doesn't work again rename the "mstask.exe" to "mstask.old", pop in your windows cd and do a repair. That should fix you up.