This happens if you try to extract part 2 or 3 first. You must start with part1.rar .
rar multipart (*.part1.rar, *.part2.rar) support? #207 - GitHub doc15.part1.rar
Ensure that doc15.part1.rar and all subsequent parts (part2, part3, etc.) are in the same folder before you begin. This happens if you try to extract part 2 or 3 first