I've just encountered this same problem after updating to ReaderX. I updated
everything possible on Microsoft without luck. What worked -- I had saved my document just to the desktop. I right-clicked on my document's file icon and selected "open with" "Adobe Reader." It popped open a license agreement for using ReaderX, which I "accepted" and then my document opened up. Miraculous! Now my PDF files seem to working just fine again. An odd little quirk. I hope this works for you too.
After my post I found some other references to the MAPI32.dll being changed and I found that the MAPI32.dll being ussed was only 7KB in size. I searched the machine for other files the same name; changed the name on the one that was there and copied one of the larger MAPI32.dll files to the /system32 folder. That larger file cured the problem.
Thanks for letting me know about your fix. I had seen a comment on another forum about double-clicking the MAPI32.exe file, but a search of my computer didn't turn that one up, at least not the .exe file, so I couldn't fix it that way. But I'll take another look and see if I find anything like your situation. I've encountered odd errors with Adobe before and had no luck in getting a response from Adobe, so I'm glad to find this forum.