Error extracting downloads

Downloaded quite a few things from here recently, but with a few I got an error when trying to extract the files.

Jamie's Essential Filters was one, and the other is the FMT Stadium Superpack.

I think there was another but can't remember at the moment, but all of them gave the same error

"Error opening archive: the archive is either in unknown format or damaged.

Sounds like an issue with incomplete download, but not sure.

Are you using WinRAR? If yes, use WinRAR and browse to where the archive is located and use the repair option directly on the archive. See if that helps.

Have you tried using 7-zip for the extraction?

Hamster ZIP Archiver and Zip opener are what I've used

Downloaded WinRAR and it worked ok for that... didn't have to do any repair though.