While trying to install SQL server 2008, the installation failed several times because of a single error that reads “The SQL Server 2005 Express Tools are installed. To continue, remove the SQL Server 2005 Express Tools.” to fix this error, I simply deleted the following registry key. SOFTWARE\Microsoft\Microsoft SQL Server\90 some say removing SQL Prompt resolved the problem but in my case I have never installed Red-Gate SQL Prompt. DISCLAIMER: Backup your registry before modifying, messing around in your registry usually leads to trouble and reformat.