Can not access MacBook Pro and MacBook Air backups

Hello,  I hope this is an easy fix?

I have a macbookpro which I backed up and sort of retired.  I also backed up my MacBook Air on the same MyBook for Mac.  They show up as two ‘drives’, I guess.

When using the Air  I am unable to access the back up datat on the Pro and Vica Versa.  I never set a password for either of them, but it seems this is protected.  If I can’t access my dayta from another computer, what is the point of having a back up like this?  I can not get to anything except from the computer to which I backed it up ‘on’.

 Can someone please help, I am very frustrated not being able to see photos I took 2 years ago on my Pro, thay are all on the MyBook which will no allow me access via the MacAir… sigh…Does this make sense? 

Thank you for enlightening me.

What drive?

What is the error message?

The backups can be opened from any computer but that will depend on the way YOU setup the backup