The 505 is compatible with Macs. When you connect it to the computer through USB it comes up as an external drive on your desktop.
Sony has their own program to maintain and syncs book to the reader that is native to the Mac of you can use Calibre (
http://calibre.kovidgoyal.net/download_osx
I prefer Calibre but, like everything, your mileage will vary.
What software are you currently using with the 505? The error message is not familiar to me but maybe the guys over at the Sony section of this forum may have seen it before (
https://www.mobileread.com/forums/forumdisplay.php?f=100 )
You may have to actually call Sony to have them de-authorize the reader for you so you can start over
