Installing SQL-Server with WiX : fails if older version is present

Hi,

I have a problem with my SQLServer 2014(Express) silent installation, in case there is a older Version e.g. SQL-Server 2012(Express) installed.

The log shows the following error:

[02DC:0C48][2014-12-04T10:53:30]i301: Applying execute package: SQLEXPR_x64_ENU.exe, action: Install, path: C:\ProgramData\Package Cache\38E0D08F06AF2F907E1AEBDCA0444B828AE356B5\SQLEXPR_x64_ENU.exe, arguments: '"C:\ProgramData\Package Cache\38E0D08F06AF2F907E1AEBDCA0444B828AE356B5\SQLEXPR_x64_ENU.exe" /ACTION=Install /INSTANCENAME=SQLExpress /FEATURES=SQL,Tools /TCPENABLED=1 /SQLSVCACCOUNT="NT AUTHORITY\NETWORK SERVICE" /SQLSVCSTARTUPTYPE=Automatic /SQLSYSADMINACCOUNTS=BUILTIN\Administrators /ADDCURRENTUSERASSQLADMIN=TRUE /Q /HIDECONSOLE /SkipRules=RebootRequiredCheck /IAcceptSQLServerLicenseTerms'
[02DC:0C48][2014-12-04T10:55:54]e000: Error 0x84bb0001: Process returned error: 0x84bb0001

Some facts:
- My setup works well, if I use a plain Windows 7/64 installation (VM)
- If I uninstall the older SQL-Server Version, setup works well also.
- The SQLServer installation is part of a WiX-Bootstrapping project

<util:RegistrySearch
      Id="SqlInstanceKeyFound"
      Root="HKLM"
      Key="SOFTWARE\Microsoft\Microsoft SQL Server\Instance Names\SQL"
      Value="$(var.InstanceName)"
      Result="exists"
      Variable="SqlInstanceKeyFound" /><util:RegistrySearch
      Id="SqlInstanceKey"
      Root="HKLM"
      Key="SOFTWARE\Microsoft\Microsoft SQL Server\Instance Names\SQL"
      Value="$(var.InstanceName)"
      Variable="SqlInstanceKey"
      After="SqlInstanceKeyFound"
      Condition="SqlInstanceKeyFound" /><util:RegistrySearch
      Id="SqlInstanceFound"
      Root="HKLM"
      Key="SOFTWARE\Microsoft\Microsoft SQL Server\[SqlInstanceKey]"
      Result="exists"
      Variable="SqlInstanceFound"
      After="SqlInstanceKey"
      Condition="SqlInstanceKeyFound" /><util:RegistrySearch
      Id="SqlVersion"
      Root="HKLM"
      Key="SOFTWARE\Microsoft\Microsoft SQL Server\[SqlInstanceKey]\Setup"
      Value="Version"
      Variable="SqlVersion"
      After="SqlInstanceKey"
      Condition="SqlInstanceFound" /><PackageGroup Id="SQLexpress2014"><ExePackage
        DisplayName="SQL Server 2014 Express"
        Cache="yes"
        Compressed="yes"
        PerMachine="yes"
        Permanent="yes"
        Vital="yes"
        SourceFile="C:\temp\SQLEXPR_x64_ENU.exe"
        InstallCommand="/ACTION=Install /INSTANCENAME=$(var.InstanceName) /FEATURES=SQL,Tools /TCPENABLED=1 /SQLSVCACCOUNT=&quot;NT AUTHORITY\NETWORK SERVICE&quot; /SQLSVCSTARTUPTYPE=Automatic /SQLSYSADMINACCOUNTS=BUILTIN\Administrators /ADDCURRENTUSERASSQLADMIN=TRUE /Q /HIDECONSOLE /SkipRules=RebootRequiredCheck /IAcceptSQLServerLicenseTerms"
        UninstallCommand="/Action=Uninstall /INSTANCENAME=$(var.InstanceName) /FEATURES=SQL /Q /HIDECONSOLE"
        DetectCondition="SqlInstanceFound"><ExitCode Value ="3010" Behavior="forceReboot" /></ExePackage></PackageGroup>    

It looks that I would need to check for older versions as well !?
If so, is there a generic way to do that?

Thanks for any hints and help.

Regards
Rainer