Exchange Server 2003

I'm trying to uninstall exchange 2003 but it keep telling me there is still an organization in the system manager. When i access the system manager i see but each time i try to remove it tells me that there is no such object and get the error code 0x80072030 (8240). I cannot run the forest prep neither it just stop without giving me an error msg. I can run the domain prep without a problem. How can i manually remove everything so i may reinstall exchange.

Thanks