What medium are you using for back-up as I have only ever come across that error with CD/DVD? Usually a scratch or dirty mark causes a misread so the checksum for a sector does not match the sum of bits read.
What software are you using to do the back-up and are they only data files that you are backing up? There must be a corrupted file somewhere so note where you get to in the back-up and see if you can isolate the file. If necessary copy files across in smaller batches so that you can find the file.
1 Start with the simplest and sometimes only solution that you need to fix the problem. Clean the DVD- and/or CD-ROM drive on your computer. Buy a lens cleaner disc and follow the instructions for cleaning the drive.
2 Retry the operation you were attempting before the error. If you are successful, the cleaning is all you needed. If not, proceed to Step 3.
3 Inspect the CD or DVD that you are attempting to use for scratches or any other form of damage. Try placing the disc in another device that you know functions properly to see if the disc is the problem. A disc that was improperly burned can cause a CRC.
4 Check all of the related cables to the drive(s) on the computer to make sure they are connected properly. Loose cables can cause a CRC error.
5 Test the CD or DVD drive to see if it might be failing. Try discs that you know are good in the drive(s) and see if the drive reads them properly. If not and you have worked through the previous steps with no success, you probably have a failed or failing drive that needs to be replaced.
6 For CRC error messages received while attempting to open files, try reinstalling the software you are attempting to open the file with or downloading the file again.
7 Troubleshoot network- or modem-related CRC errors by verifying that you have a good connection, checking that you are using the proper file format and then retrying the transmission.