Unable to access folders on drive

I am running OS X Yosemite 10.10.5 and have a My Book for Mac external HD (I think 3TB?) connected. I am getting this message – “The folder “Pictures” can’t be opened because you don’t have permission to see its contents.” for all of the folders containing my backed up files. I have tried “Get Info” and changing permissions, but am still getting the red - symbol in the lower right hand corner of the folders. I did scroll down through the message board, as I am sure this has been addressed before, but did not find the topic. Any help would be greatly appreciated. Thank you.

How did you add your files to your external hard drive? Are you able to open your files if you copy them to your desktop?

It is automatically backed up via the Time Machine program on my Mac.