I have the same problem on my QNAP NAS. I am a long term Windows user – having been using Mac for past 3 years. This read/write problem and permissions is a constant pain. No-one seems to have the answer.
I can access the NAS on my Windows machines with no problems at all. All permissions are set correctly on the NAS. I am the sole user of the MAC and am, therefore, the admin. I should have full permissions for all MY drive and the files they contain. This is just not the case.
For an OS X touted to be the most advanced in the world – it is a mess. Permissions is a fundamental thing that should just work. The user should not be having to repeatedly mess around with disk utility of the terminal.
Not much more hair left to pull out.