Bitmaps disappeared while working on imported pdf

[jimhanus]

I have imported a page-size pdf into WD6 and have been modifying it to re-use. I'm almost finished with it, but when I looked at it today, 7 of the bitmaps (approximately half of them) are missing as indicated by the generic image placeholder (see attached). The file wasn't closed, nor was WD6 closed and restarted. Any suggestions why this might have happened, or where those bitmaps might be, before I start the project over?? Original file wasn't made with Xara.

Jim