Getting domain not available, unable to login error message

I have a small office which has around 11 workstations connected to an Windows 2003 server. The server acts as a domain controller and there are some document software which are installed on the workstation. The data stores in the server. To run the application I had provided everyone a Z drive. This is an shared directory for the users. When the user login in the system, they can see the Z driver in My Computer and can run the application from there. Some of the clients have automatic domain login but the user groups are different for them. It was working fine. There were some updates in the server and after that many of my client system are facing an error saying that the domain controller is not found. They can no longer be accessed the network drive also which automatically leads to a crash of software. I tried searching a lot about the error but does not found any major issue. How to fix this error out. I do not have to re-install everything back again.

There is an easy fix for that. First check that your domain settings are not changed. Second go in each client system and login with the administrator account. Then right click on my computer > properties > and configure computer name and domain each of them again. Restart and check.

The computers which are connected to the domains are cloned in such a way that they are provided with an SID. If this SID/network id is changed then you face that error. It is an kind of serial number of each client system. When you connect any system first time to the domain you go through an process of getting an Network ID for the workstation. Once that process is done properly the user can connect to the domain. You can try back creating those back again. The same method that is mentioned above will work. You can try each system reconnecting again and fix the issue out. There is no need to do any changes to the server. This can be just because the computer has lost its network id on the server.

In the login box there is an drop down arrow from where you have to choose the domain. Just check that you can see that. If not then verify the server lan connection. I think it can be due to cable fault.

Updates do no changes in the server. The client system has logi account in the domain and you can check the setting via Active Directory. Go in Active Directory and just see that all users are listed in that or not. Second check rights of the group of users that you allowed to login on Domain. The other reason behind can be due to name resolution. Set your system tcp ip settings on default and right click on the network connect > repair. Also properly verify the dns of the system, check that it is working properly or not. If not then you can run some commands like netdiag /debug to check the status. Restart server. There are also many other Active Directory troubleshooting tips that can help you for the same error.

Just check any of your user has not moved the computer to an different place. The error also occurs if there are computers with similar names available on the same network. If yes then rename them. It is always better to have a network chart with you with each computer named in serial wise.

The exact cause of this error is due to security identifier. It is a key which allows the server to identify a workstation. And if this is delete accidentally from the Active Directory domain, then you get that error. The error also occurs when you use tools like Norton Ghost and run the same image file on many other computers on the same network. You can fix this by deleting the computer from Active directory and then re-adding the same.

Change the computer name and then try back. It will surely work. There is an option for repair when you right click on the active lan connection. Choose that to fix the ip and other issue. Also verify that the server can communicate with the computer. This is just for ensuring that your lan is working. Do not forget to reboot the system after every proper account configuration.