Share Security mode is EOL and not available on any newer ReadyNAS models. Share mode doesn't work well with new OSes.
Take a look at How to Migrate to User Security Mode
What version of RAIDiator did you update from?
Note that it's possible that your issues could be related to the ownership issue introduced in 4.1.9. You may wish to downgrade to 4.1.8 or update to 4.1.10 beta, then fix the ownership via Shares > Share Listing > Sharename > CIFS, click on Advanced Options tab, set the user and group you want to own the share, click Set Permission for existing... and click Apply. I think this tab isn't available in Share mode so you would need to change to User mode to use it.
In 4.1.9 Netatalk (provides AFP service) was updated to Netatalk 2.2.3 which has improved compatibility with Mac OS X Lion.