Error when attempting to install Windows SDK 7.1

Question

I have not been able to install Windows SDK 7.1 (the machine runs Win 7 Pro x64).
The error message shows up in a message box as:
"SDKSetup encountered an error: Input string was not in a correct format."
By browsing to my %TEMP% directory, I find log files as mentioned at http://stackoverflow.com/questions/1901279/windows-7-sdk-installation-failure
Sample content:
16:52:06 Friday, 06 February 2015: -------------------------------------------------------------------------------------------------
16:52:06 Friday, 06 February 2015: [SDKSetup:Info] Begin
16:52:06 Friday, 06 February 2015: [SDKSetup:Info] SDKSetup Version 7.1.7600.30111
16:52:09 Friday, 06 February 2015: [SDKSetup:Info] Beginning download of file http://download.microsoft.com/download/A/6/A/A6AC035D-DA3F-4F0C-ADA4-37C8E5D34E3D/setup\SDKSetup.cab to C:\Users\[username]\AppData\Local\Temp\SDKSetup\SDKSetup.cab
16:52:09 Friday, 06 February 2015: [SDKSetup:Info] Successfully downloaded the file http://download.microsoft.com/download/A/6/A/A6AC035D-DA3F-4F0C-ADA4-37C8E5D34E3D/setup\SDKSetup.cab to C:\Users\[username]\AppData\Local\Temp\SDKSetup\SDKSetup.cab
16:52:09 Friday, 06 February 2015: [SDKSetup:Error]: Input string was not in a correct format. Stack:    at System.Number.StringToNumber(String str, NumberStyles options, NumberBuffer& number, NumberFormatInfo info, Boolean parseDecimal)       at System.Number.ParseInt32(String s, NumberStyles style, NumberFormatInfo info)       at System.String.System.IConvertible.ToInt32(IFormatProvider provider)       at System.Convert.ChangeType(Object value, Type conversionType, IFormatProvider provider)       at System.Data.XSDSchema.HandleElementColumn(XmlSchemaElement elem, DataTable table, Boolean isBase)       at System.Data.XSDSchema.HandleParticle(XmlSchemaParticle pt, DataTable table, ArrayList tableChildren, Boolean isBase)       at System.Data.XSDSchema.HandleComplexType(XmlSchemaComplexType ct, DataTable table, ArrayList tableChildren, Boolean isNillable)       at System.Data.XSDSchema.InstantiateTable(XmlSchemaElement node, XmlSchemaComplexType typeNode, Boolean isRef)       at System.Data.XSDSchema.HandleTable(XmlSchemaElement node)       at System.Data.XSDSchema.HandleParticle(XmlSchemaParticle pt, DataTable table, ArrayList tableChildren, Boolean isBase)       at System.Data.XSDSchema.HandleComplexType(XmlSchemaComplexType ct, DataTable table, ArrayList tableChildren, Boolean isNillable)       at System.Data.XSDSchema.InstantiateTable(XmlSchemaElement node, XmlSchemaComplexType typeNode, Boolean isRef)       at System.Data.XSDSchema.LoadSchema(XmlSchemaSet schemaSet, DataSet ds)       at System.Data.DataSet.ReadXmlSchema(XmlReader reader, Boolean denyResolving)       at SDKSetup.SDKSetupDll.LoadConfiguration()       at SDKSetup.SDKSetupDll.Init(List`1 sourceFileLocations, Boolean quiet, Boolean showHiddenFeatures, InstallModeType installMode, List`1 featureParams, List`1 productParams)       at SDKSetup.SDKSetupDll.RunSetup(List`1 sourceFileLocations, String logFileName, String loggingSwitches, Boolean quiet, Boolean showHiddenFeatures, InstallModeType installMode, List`1 featureParams, List`1 productParams, List`1 DisabledFeatures, Boolean sqmOptInFromCmd, String installLocation, String installLocationSamples, Boolean ignoreDependentProducts)
16:52:12 Friday, 06 February 2015: [SDKSetup:Info] End
16:52:12 Friday, 06 February 2015: -------------------------------------------------------------------------------------------------
I tried both the web installer and the ISO image file (the x64 version), with the same result, except that the ISO file omits the downloading step in the log file. 
Note:
I have one version of the Microsoft Visual C++ 2005 Redistributable (x64) installed, and one version of the Microsoft Visual C++ 2008 Redistributable (x64) installed.  No 2010 (or later) version — see http://blogs.msdn.com/b/vsnetsetup/archive/2012/03/14/unable-to-install-microsoft-windows-sdk-for-windows-7-and-net-framework-4.aspx. 
I then noticed it is required to have Microsoft .NET Framework installed, so I installed version 4.5.2. 
This did not affect the results.  I got the same error message, and the same logged events. 
Clean boot did not resolve this.  Repairing the .NET Framework installation did not resolve this.
Thanks for any guidance,
   DIV

Answer 1

You need to know what you have already.
Open Disk Utility, go to the First Aid tab, take a screenshot of the lefthand sidebar.
I won't advise on partitioning until I know what is there. (The BCA page where you create the partition will not show whether there is another, it will just fail if there is)