I have lost a number of photographs from my Lightroom library. When I try again to import them (all jpeg), I am told that they can not be imported because they can not be read. Is there a fix?
"Cannot be read" indicates that the destination folder (as specified in the Import dialog box) does not have WRITE permission. Change your permissions.
The idea that you would want to re-import photos that you have previously imported is not a good one, there are many drawbacks to this approach. I'm not sure what you mean when you say "I have lost a number of photographs...", but there are probably better solutions than re-importing.