Finally I applied the LMGTFY principle (the 21st century version of RTFM), I did a web search on the message, which eventually led me to this nice article on superuser.com. The short version of The Answer is:
gs -o FIXED.pdf -sDEVICE=pdfwrite -dPDFSETTINGS=/prepress CORRUPTED.pdfThat↑ worked great for me, though someone recommends instad -dPDFSETTINGS=/default.