Installing Update Rollup 6 for Exchange Server 2010 Service Pack 2 fails

I've managed to fix this by manually removing every trace of Exchange on this server (not all steps were found at my server but i post them anyway). And kids don't do this at home. This is not supported and may harm your system. I was desperate:

1. Run setup /m:uninstall
2. Stop and disable all the Exchange 2010 services
3. Use Registry Editor (Start->Run->Regedit) to remove these Exchange related registry keys:
   * HKLM\SOFTWARE\Microsoft\Exchange
   * HKLM\SYSTEM\CurrentControlSet\Services\MSExchange* (all the keys starting with “MSExchange”)
   * HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\Microsoft Exchange
4. Remove the entire Web Server role (don’t forget to reinstall afterwards as it’s a prerequisite for E2K10!)
5. Remove the Exchange 2010 server from Active Directory. I ended up deleting the entire “Microsoft Exchange” branch from ADSIEdit (Configuration Container > Services > Microsoft Exchange) as my Org only counts one server.
6. Use Windows Explorer to delete:
   * C:\Program Files\Microsoft\Exchange Server
   * C:\ExchangeSetupLogs
7. Use Windows Installer CleanUp Utility to remove all the exchange related info from the installer database.
8. Remove the security groups created by Exchange setup from AD
9. Use CC Cleaner to remove registry entries for Exchange

I also found this link which gives a bit bigger overview: http://msexchangehelp.wordpress.com/2010/02/10/manually-uninstall-last-exchange-2010-server-from-organization/

Anyways it solved the problem that installation went thru but again I am at square one with corrupted installation since Hub Transport failed to install AGAIN. So redoing this steps again... and trying installation again with IPV6 disabled.

Did you update the Active Directory schema for Exchange 2010 as per this Microsoft Exchange 2010 forum link with a similar problem?

See Exchange Server 2010 Planning and Deployment - Prepare Active Directory and Domains for more info on the steps.