Active Directory Troubleshooting

We are running Active Directory on Windows Server 2003 with about 40 agents. We recently have a situation where the agents are getting logged out with an error and we have to reboot the server before they will be able to get back in. This happens every couple of hours and we need someone to log in to our system and troubleshoot and help us determine what is causing this and find a solution. We do have a backup Active Directory that should be replicating but not sure if the errors are affecting this or not. We have been using the Active Directory with this set up for over 6 months with no issues and suddenly we have this issue. We need someone that can work with us during our hours of operation 7:30AM-5:00PM CST M-F to work on this. We need someone as quickly as possible (tomorrow morning if possible)