Error Code 5 is basically a flatline.
You could try a service like Markzware, see if they recover your file by converting it to quark and back again (I know seems like a very wrong work flow).
But I've heard of this working in the past. I think they'll do the conversion for you and if it works you will need to pay the going rate for the files back (not 100% sure on how they work but that's my understanding)
The poster also posted in the Acrobat forum about whether the corrupted InDesign files could be recreated by exporting InDesign files from PDF files he has in Acrobat. I said no, but suggested Recosoft's great (but not cheap) PDF2ID product for reconstructing the documents from the PDFs if they're critical documents.