After the upgrade failed, I tried to remove all the older SQL Server (2008 &
2008 Express).
Now the installation fails with strange errors (account for analysis server
not found, log file could not be written, ...).

How to do a clean installation?

Thanks

Hi Eric,
This issue may be caused by uncleaned installer information. After you
remove your SQL Server 2008 from Add/Remove Programs, please try using
Windows Installer Cleanup utility to remove left installer information on
SQL Server 2008,http://support.microsoft.com/default.aspx/kb/290301?p=1.

After you clean the left SQL Server 2008 installer information, try
restarting your computer and then install SQL Server 2008 R2. Hope this
helps.

Best regards,
Charles Wang