Just solved my problem with RIS clients not joining the domain following our recent upgrade to Windows Server 2008 on our domain controllers.
Aside from the obvious checking that you have got correct DNS, DHCP, domain names, etc check out the following Microsoft KB Article.
http://support.microsoft.com/kb/942564
Look for the following lines in your NetSetup.log file to indicate that this is the problem.
11/09 02:21:04 Failed to validate machine account for ComputerName against SPN_Name: 0xc0000388 11/09 02:21:04 NetpJoinDomain: w9x: status of validating account: 0x4f1
All working again now. Now off to set up a load of laptops for new staff. :-)
Thanks I’m experiencing this since putting in a 2008R2 DC. Nice to find the answer to fixing it.