I found the following information. You might use WinRAR to try what is suggested.
If you have a RAR (or ACE) archive and receive CRC errors or an "archive damaged"-type message when you attempt to extract it, there may be a possibility of repairing that damaged archive: It needs to be complete (not short any bytes) and it needs to have been created with a recovery record.*To see if it was, click on the "Info" button in WinRAR. If it was created with a recovery record, then you have a chance: highlight the damaged file in the WinRAR (or WinACE) window and click on the first-aid box with the red cross,* the "Repair" icon in WinRAR. In WinACE click on 'Archive', then 'Repair Archive'. In both cases a window will pop up asking you where to put the file the program will create in it's attempt to make a perfect file. Usually you have it put the "repaired" file in the same folder as the rest of the archive.* It might be able to create a perfect file, which you can then rename to take the place of your damaged one, and retry the extraction process.
If the damaged file has no recovery record, then no repair is possible. If it is short bytes, even if there is a recovery record,* then no repair is possible. There are no third-party products (at this writing) for repairing ACE or RAR files other than the PAR1 or PAR2 systems. WinRAR has it's own parity-archive system if the archive creator used it- this is shown by there being REV files, and if present, WinRAR will use them to repair or replace the damaged files. If not, then there is little hope of repairing the entire archive, but you still might be able to extract individual files from it.