This "Windows could not apply unattended settings during pass (null)" error is generated by multiple causes, among which, the most frequent one is having dual-architecture unatend.xml files.

The structure of the XML file requires that the user specifies the system  processor architecture, either i386 or amd64 (not both), like in the following example (setup language setting):

<component name= "Microsoft – Windows – International – Core – WinPE" processorArchitecture= "amd64" publicKeyToken= "31bf3856ad364e35" language= "neutral" versionScope= "nonSxS" xmlns : wcm= "http://schemas.microsoft.com/WMIConfig/2002/State" xmlns : xsi= "http://www.w3.org/2001/XMLSchema-instance">
            <SetupUILanguage>
                <UILanguage>en-US</UILanguage>
                <WillShowUI>OnError</WillShowUI>
            </SetupUILanguage>
            <UserLocale>en-US</UserLocale>
            <SystemLocale>en-US</SystemLocale>
            <UILanguage>en-US</UILanguage>
            <UILanguageFallback>en-US</UILanguageFallback>
            <InputLocale>en-US</InputLocale>
</component>

Now, there’s often the case when multiple components are needed, like this:

<component name= "Microsoft – Windows – International – Core" processorArchitecture = "amd64" publicKeyToken= "31bf3856ad364e35" language= "neutral" versionScope= "nonSxS" xmlns : wcm= "http://schemas.microsoft.com/WMIConfig/2002/State" xmlns : xsi= "http://www.w3.org/2001/XMLSchema-instance">
    <InputLocale>en-US</InputLocale>
    <UILanguage>en-US</UILanguage>
    <UILanguageFallback>en-US</UILanguageFallback>
</component>
<component name=" Microsoft – Windows – Shell – Setup" processorArchitecture= "i386" publicKeyToken= "31bf3856ad364e35" language= "neutral" versionScope= "nonSxS" xmlns : wcm= "http://schemas.microsoft.com/WMIConfig/2002/State" xmlns  : xsi= "http://www.w3.org/2001/XMLSchema-instance">
    <OEMInformation>
        <Manufacturer>Whatever</Manufacturer>
    </OEMInformation>
    <ComputerName>*</ComputerName>
    <DisableAutoDaylightTimeSet>false</DisableAutoDaylightTimeSet>
</component>

The above example will generate the "Windows could not apply unattended settings during pass (null)" error, because of the processorArchitecture declaration mismatch. So, if your file is for amd64 architecture, make sure no i386 entries are left in the file, and vice versa.

This article applies to Microsoft Windows Vista, Windows 2008, Windows 2008 R2 and Windows 7.

Note: do not Copy/ Paste the XML code above, since I had to reformat it, so that it displays better. As such, the code is not parsable.