You may need to reformat the SSD. Note that when you reformat a drive it erases everything off it. To format the drive, go to the Disk Utility app on your MacBook. Select the SSD in the left-hand column, then click on "Erase". At this point you can rename the SSD and then choose a format from the drop-down menu. If you intend to use this drive exclusively on Mac devices, you should format the drive in "Mac OS Extended (Journaled)", but if you want to use the drive between Macs and PCs, you need to use the "ExFAT" format. Finally, click on "Erase". Always remember to eject your SSD before unplugging it from your computer. Not doing so could damage the SSD or the files on it. Hope this helps.