ReadyNAS 4200 Unable to Join Domain

Hi,

We have two ReadyNAS 4200 storage devices which we are trying to connect to the domain. They were previously on the domain but we have since migrated to a new domain controller with new DNS servers. 

I have gone into Network>Global Settings and added our new DNS servers in there. 

Then in Security>Security Mode>Domain> I set:

• Domain type: ADS
• NetBIOS Name
• Domain Name
• New object OU (I tried with and without this)
• Typed in the new domain controllers IP address under "Domain Controller:"
• Input a Domain Admins user credentials. 

When I click apply Unsuccessful joining domain our-domain-name

I've downloaded the logs and in domain_join.log it has the following error:Failed to join domain: failed to lookup DC info for domain 'our-domain-name' over rpc: NT_STATUS_CONNECTION_RESET

From a computer on the network I can do nslookup the IP addresses of the NAS units and it resolves their hostnames. 

If anyone could offer any advice I would greatly appreciate it. 

Thanks,
Jacob