I had a similar problem when I first started using MS Reader and the book was on the SD card. I couldn't read more than a 100 pages before getting that message. My problem was that I had to soft-reset because I couldn't restart MS Reader after exiting -- tapping the icon would do nothing, and there was nothing running in memory.
Long story short, I followed the directions in here:
http://www.microsoft.com/reader/info...c.asp#nolonger and deleted the proper EBO file. Then I loaded the book back up and let it paginate until it was complete without going into standby. I'm not sure but maybe I turned it off/standby before it was done the first time so it was a corrupt file? Anyway, the next time I read it, I didn't get the message, so it worked for me. I don't know the root of the problem, but I hope that helps