Quit Adobe Digital Editions.
Navigate to /Users//Library/Application Support/Adobe/Digital Editions and drag the activation.dat file to the trash.
If you are using 10.7, see Access hidden user library files | Mac OS 10.7 and later
Open Adobe Digital Editions and reauthorize.
The authorizing worked: I found activation.dat and dragged it to trash.
After reauthorizing in Adobe digital editions I opened "Reader for Mac" and I was asked
to authorize my computer and this didn't work.
Any further suggestions?
Reader for Mac is a program from Sony not from Adobe. Should ask in a Sony Forum or Sony Support.