15-6-2008 23:14:16 : Could not open document - Document appears to be damaged and needs to be re-saved : F:\DocumentStore\WorldDomination\UndergroundLair\Plans\RestRooms\italian bathroom fixtures.pdf

I get the above error reasonably often during Adobe .pdx index builds, can anyone shed some light? Is this common for anyone else?

Any idea what is causing it for a few dozen out of hundreds of thousands of pages?