You are getting this error when doing what?
What XP service pack level do you have?
The first thing I would try if I encountered such a strange error is to run the system file checker:
I'm running XP with sp3. After downloading Reader 10 I get the error when attemps to run. I just downloader Reader 8.2.0 and it runs fine. Maybe I'll just stick with that and be thankfull.
Run the fixmapi.exe application in windows\system32 directory and thats it.
I was having the same problem with my sister's machine a couple of weeks ago. I found that the MAPI32.dll in use was only 7 KB. I found other, larger MAPI32.dll files in other directories, I copied one of those to the /system32 directory where the small file was and that corrected the problem.