I get an error like "Unknown method in filename"!
Older WinRAR versions (< 2.90) don't have the improved compression methods found in WinRAR 3.0 and above.
Either a RAR 3.0 archive is being unpacked by RAR 2.8 or older or a ACE 2.0 archive is being unpacked by WinRAR 2.8 or older.
In this case please update your old WinRAR/RAR version to the actual release.