Machine can't join domain - DC could not be contacted.

Almost always when there is such a problem, it is because the DNS server isn't set to the dc. No other nameserver should be assigned.

"it is because the DNS server isn't set to the dc. No other nameserver should be assigned."

I'm not certain what you mean there. the DNS server should have the DC's as its DNS entries  ? 

In this case the DCs ARE also DNS (Its a tiny network) 

the DC network setting have 127.0.0.1 and the other DC's IP  (also DNS) 

These are in the BPA on the server

MYDC   Error   DNS: Zone WTPscada secondary servers must respond to queries for the zone.   Configuration

MYDC   Warning   DNS: Zone WTPscada secondary server 192.168.13.225 should respond to queries for the zone.   Configuration

MYDC   Warning   DNS: Root hint server 128.8.10.90 must respond to NS queries for the root zone.   Configuration

MYDC   Warning   DNS: Root hint server 128.63.2.53 must respond to NS queries for the root zone.   Configuration

MYDC   Error   DNS: The DNS server 192.168.13.225 on  VLAN 13 must resolve names in the forest root domain name zone   Configuration

MYDC   Error   DNS: The DNS server 192.168.13.225 on  VLAN 13 must resolve names in the primary DNS domain zone   Configuration

MYDC   Error   DNS: The DNS server 192.168.13.224 on  VLAN 13 must resolve names in the primary DNS domain zone   Configuration

MYDC   Error   DNS: The DNS server 192.168.13.224 on  VLAN 13 must resolve names in the forest root domain name zone   Configuration

MYDC   Warning   DNS: Root hint server 128.9.0.107 must respond to NS queries for the root zone.   Configuration

MYDC   Warning   DNS: Root hint server 198.32.64.12 must respond to NS queries for the root zone.   Configuration

MYDC   Warning   DNS: Zone WTPscada secondary server 192.168.13.224 should respond to queries for the zone.   Configuration

MYDC   Warning   DNS: The DNS server should have scavenging enabled.   Configuration

MYDC   Error   DNS: DNS servers on  VLAN 13 should include the loopback address, but not as the first entry.   Configuration

In the NIC's settings, you should have exactly one nameserver assigned, your DC. If there is any other assigned, you'll get issues. If your DHCP server is setup properly, & your PC isn't using a static IP, you should have no problems.

There is no DHCP and I have 2 DC's  Client is configured with both DNS entries

(there are only 20 clients on this network)

Since DNS is on both my DC's, are you saying I point DC1's DNS to DC2 and vice versa? 

Any chance the Short domain name is a problem now, where it wasn't previously?

If I were you I would setup a DHCP Server. It makes everything a lot easier, & you don't have to setup a static IP for every device you want to connect to the LAN. Remember that you can't share an IP between different devices, & if you have to manage all of those yourself, you'll be bound to make mistakes. A DHCP server makes sure that doesn't happen. You can also configure it to assign a static IP based on the MAC address of a device, if that device needs such an IP (Servers, Printers etc.). A DHCP server should also make sure there aren't any external DNS servers assigned, which would cause your problem.

That's not an option, this is industrial application and DHCP is not well tolerated. 

I do understand the basics of networking and vlans and the static IPs are well documented. There are no duplicates. 

This is an unusual AD thing that's happening. Its not a simple misconfiguration of a client - it's something under the covers.