If the RAR archive that you downloaded has any corruption, you might get the “archive damaged or incomplete” error message when you try to extract the files it contains. This is a common problem because many RARs are first uploaded to Usenet, which doesn’t have built-in error correction.
On Usenet, data integrity is insured by posting some PAR files along with the RARs. However, people often download the RARs from Usenet, and then upload them to some other system separately from the PARs.
So, the solution to this problem is to go back to wherever you got the RARs and look for the associated PAR files. Once you have them, you can run them through SuperNZB’s free PAR decoder and repair your RARs.