You might get this error message when trying to extract a file from a RAR archive. If you downloaded the RARs from Usenet, you might be able to fix the problem by downloading the associated PAR files, which can magically fix RAR files. Usenet does not have automatic error checking, so PAR files are almost always posted along with RARs.
If you have never heard about Usenet, you can learn to download RARs with the NZB method here.
RAR archives almost always consist of more than one file – or “segment”. So, you want to make sure that you have all of the segments. Looking at a RAR file, it’s not obvious how many more there are in the archive set. However, if you can find the associated PAR2 file, it will show you the list of all the files in the archive.
If you didn’t download the RAR files from Usenet, keep in mind that the files may have originated on Usenet. For example, somebody may have downloaded a RAR archive from Usenet, and then uploaded it to BitTorrent, but forget to include one of the segments. So, the same advice applies: look for more segments and/or the associated PAR files.
Keep in mind that RAR archives are made by people who sometimes make mistakes. So, it is possible that you have an unusable file because the creator forgot to do something such as upload all of the segments.