Does this happen only on torrents you are downloading, or does it also occur on ones you are seeding? The CRC (Cyclic Redundancy Check) is something that is done to verify that the data in the torrent is correct (basically). Either your hard drive is beginning to fail and writing or reading data incorrectly, or it's possible there is an issue with your network, causing packets to incorrectly download or upload. Your answer to my previous question will help narrow it down. Have you experienced any odd issues with your hard drive and about how old is it?
It is also possible your ISP is attempting to interfere with your torrent downloads by feeding Tixati incorrect information. You can check that by pausing any downloads or uploads you have and by going to this site:
Then hit the "Start Testing" button.