CRC errors (Cyclic Redundancy Check), indicate that the file has become corrupt, either at the time of compression or while being transfered. CRC software calculates a short, fixed-length binary sequence, known as the CRC code for each block of data and sends or stores them both together. When a block is read or received the device repeats the calculation; if the new CRC does not match the one calculated earlier, then the block contains a data error and the device may take corrective action such as rereading or requesting the block be sent again. However sometimes this is not possible as the data has become to corrupt.
you can try use this tool, (rar repair)
http://www.rar-repair-tool.com/
some times it's really helpful, also try to unrar it using ( keep broken files)
