You have to ensure the drive where you are keeping your ScPrime folders has the proper file system and layout. It will most likely either be NTFS or exFat. It’s very common for external drives to be exFAT. In order to be able to compress a folder, the hard drive must be NTFS and the partition style must be GPT. If the drive is not NTFS, you will have to format it. Also if the partition style is not GPT, you will have to delete the drive's partition and create a new one. The file system is easy to find out on the general information tab of the drive, as shown above.