I had this happen 2 time in the last 24 hours. A workstation is either logged on for the firs time of the day or a application stops responding and the workstation is rebooted and when the user tries to logon to the domain they can not. Upon loggin onto the PC as the local administrator the PC is nolonder a domain memeber. When you try to rejoin the domain you get a duplicated oject exists message. What is going on?

Well this isn't really an Exchange issue, but I would log onto the local computer as an administrator and check your event logs for errors this is always a helpful place to start. I would also double check your DNS settings on the local computer to make sure they are pointing to your DNS server(s), which should be an internal address. I don't know how many times I have seen someone setup the local computer with the DNS address of thier ISP thinking it is ok. Also try clearing out the cache on your DNS server as well as check the logs on the DNS server for any errors. This should get you pointed in the right direction for now without any specific errors it is a kind of hard one to answer right off the bat.One thing I just thought of....Make sure you have antivirus that is installed, running, and up to date. Hope this helps some.

As mentioned, this isn't an exchange issue, but the most common cause for this is not running sysprep with the option to change the GUID when creating a workstation image on whatever software you use to image computers.

This one is really simple Mike, First the reason your getting that error is because like the message says you have a duplicated object on the domain. What does that mean? Well that most likely that you have two computers with the same nametryingtojointhedomainwhichwhenyoutrytojointhesecondcomputerwiththesamenameittellsyouthatitcannotbecauseitisduplicatedonthenetwork. You have two optionsEither you rename the computer that your trying to add. or you delete the computer name object from active directory, join the computer your currently adding to the domain and rename the other one. Have fun.