It just started today. I checked out the Aperture preference,
I don't recall seeing that error. Does it only happen for that one image? Maybe something has become corrupted? If it is happening for all images then that is a different issue.
Thanks for the response. I think it might be something to do with the external drive (a quick google suggests that I'm not the only one to get this error message.
Wouldn't it be helpful if some of these error messages also included some suggestions about what may have gone wrong? Grumble, grumble, grumble...