If I have no idea what to do, then I usually apply powerful solution as [http://download.cnet.com/Recovery-Toolbox-for-RAR/3000-2250_4-10666647.html|rar fix tool]
You can try this:
1) Open the WinRAR application. Click on “File” and then “Open Archive” and browse to the damaged RAR file.
2) Press “Alt” + “R” on your keyboard. This will bring up the WinRAR repair dialog screen.
3) Designate an easy-to-find location in the “Folder to put the repaired archive” box.
4) Check the box that says, “Treat the corrupt archive as RAR.”
5) Press the “OK” button. Once it has finished repairing, a new archive will be built and placed in the location you designated.