When you install SQL Server 2014 set support rules would fail in “SQL product installation rule” with below error

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Rule Check Result
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Rule “Previous SQL product installation” failed. Â
A SQL product other than SQL Server 2014 CTP1 is detected. You cannot install this release until the existing instances of SQL products are uninstalled.

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OKÂ Â Â
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Cause

SQL Server 2014 CTP 1 is prerelease software and should be installed only on a clean machine with no other SQL Server instance.

More details in http://msdn.microsoft.com/en-us/library/dn169381(v=sql.15).aspx

Extract from above link

{

1.1 Limitations and Restrictions in SQL Server CTP 1

Issue: The following sections define the limitations and restrictions that apply to SQL Server CTP 1.

1.1.1 General limitations and restrictions

• SQL Server 2014 CTP 1 is prerelease software and should be installed only on a clean machine.

• SQL Server 2014 CTP 1 is a NON-PRODUCTION release and should not be installed and used in production environments.

• SQL Server 2014 CTP 1 may contain branding from Microsoft SQL Server 2012 and is versioned as 11.0.

• SQL Server 2014 CTP 1 is only available in the English language.

• Microsoft SQL Server 2014 CTP 1 is not supported by Microsoft Customer Services and Support (CSS).

}