This is an error message given by WinRAR when your RAR files have some damage. If the RAR files contain video, sometimes you can just open them with a video player and play them anyway.
In most cases though, you will want to look for the associated PAR files, which are almost always posted along with RARs on Usenet. Once you download the PAR files, you can use the free PAR decoder in SuperNZB to fix your RAR files. Just throw the PAR files into the same folder as the RAR files, and SuperNZB will use the error-correction data in the PAR’s to repair the RAR’s. This will work as long as you have enough PAR files to fix the damage.