Wix Burn, how do I allow downgrading?

Question

So I've got a pretty simple burn installer, primarily to include .net upgrades or occasionally a driver pack for hardware our app needs to talk to.

The MSI's we create support upgrading or downgrading.

<?xml version="1.0" encoding="UTF-8"?>
<Wix xmlns="http://schemas.microsoft.com/wix/2006/wi"       
     xmlns:bal="http://schemas.microsoft.com/wix/BalExtension">
    <Bundle Name="My App Name" Manufacturer="Company Name" Version="!(bind.packageVersion.MyAPP_MSI)"
            IconSourceFile="MyIcon.ico"  DisableModify="yes" DisableRemove="yes"
            UpgradeCode="{15E598EF-89CE-470B-8CEF-E32C8983DA33}" >
        <BootstrapperApplicationRef Id="WixStandardBootstrapperApplication.RtfLicense" >
            <bal:WixStandardBootstrapperApplication
                LogoFile="$(var.CoreComponents.TargetDir)InstallerGraphics\Bootstrapper_Logo.png"
                LicenseFile="$(var.CoreComponents.TargetDir)AppRoot\App License.rtf" 
                SuppressOptionsUI="yes" />
        </BootstrapperApplicationRef>

        <Chain>
            <PackageGroupRef Id="NetFx451Web"/>

            <MsiPackage DisplayName="My full Application Name"  Id="MyAPP_MSI" SourceFile="$(var.Installer_MyAppMSI_TargetPath)"
                        DisplayInternalUI="yes" ForcePerMachine="yes" Visible="yes" />

        <MsiPackage DisplayName="My Hardware Driver" Id="Installer_MSI_Driver" SourceFile="$(var.Installer_Driver.TargetPath)"
                    DisplayInternalUI="yes" ForcePerMachine="yes" Visible="yes" />

        </Chain>
    </Bundle>
</Wix>

We typically have beta releases and when a user wants to downgrade from a beta back to our stable releases they can't simply execute the old EXE installer. They have to remove previous package from Add/Remove Programs explicitly to installer the older Burn EXE.

This wasn't an issue with the MSI based install. How do we get back to that functionality?

Log

[0CB8:067C][2014-06-23T11:10:04]i001: Burn v3.8.1128.0, Windows v6.1(Build 7601: Service Pack 1), path:\\iop-filesvr\IOP\Builds\Main\8.1.240\IO Practiceware Client Setup.exe, cmdline: '-burn.unelevated BurnPipe.{197B8193-6EFC-4ED0-AF90-DE7205F13E65} {CD23A8AB-520B-4F5D-BCB9-98998C5A1EC0} 2216'

[0CB8:067C][2014-06-23T11:10:04]i000: Setting string variable 'WixBundleLog' to value 'C:\Users\jeff\AppData\Local\Temp\IO_Practiceware_Client_8.1.240.0_20140623111004.log'

[0CB8:067C][2014-06-23T11:10:04]i000: Setting string variable'WixBundleOriginalSource' to value '\\iop-filesvr\IOP\Builds\Main\8.1.240\IO Practiceware ClientSetup.exe' 

[0CB8:067C][2014-06-23T11:10:04]i000: Setting string variable 'WixBundleName' to value 'IO Practiceware Client 8.1.240.0'

[0CB8:067C][2014-06-23T11:10:05]i100: Detect begin, 2 packages

[0CB8:067C][2014-06-23T11:10:05]i000: Setting string variable 'PrerequisitesVersion' to value '1.0.0.0'

[0CB8:067C][2014-06-23T11:10:05]i102: Detected related bundle: {8d398d25-606f-419a-9b29-e3434aeb2485}, type: Upgrade, scope: PerUser, version: 8.1.241.0, operation: Downgrade

[0CB8:067C][2014-06-23T11:10:05]i103: Detected related package: {7EA877FF-CE7A-49CE-8F76-D5A11EA7DD7A}, scope: PerMachine, version: 1.0.0.0, language: 0 operation: MajorUpgrade 

[0CB8:067C][2014-06-23T11:10:05]i103: Detected related package: {8E8A7689-FB1C-4FE5-AF7C-95D499A342DE}, scope: PerUser, version: 8.1.241.0, language: 0 operation: MajorUpgrade 

[0CB8:067C][2014-06-23T11:10:05]i101: Detected package: PrerequisitesMsi, state: Absent, cached: None

[0CB8:067C][2014-06-23T11:10:05]i101: Detected package: ClientMsi, state: Absent, cached: None 

[0CB8:067C][2014-06-23T11:10:05]i199:Detect complete, result: 0x0 

[0CB8:076C][2014-06-23T11:10:16]i000: Setting numeric variable 'EulaAcceptCheckbox' to value 0

[0CB8:076C][2014-06-23T11:10:16]e000: Error 0x80070666: Cannot install a product when a newer version is installed.

Answer 1

Try to add <Property Id="REINSTALLMODE" Value="amus" /> in your product.wxs file. REINSTALLMODE property is a set of settings which defines the behavior of new installation with different/same version. For more details, you can check REINSTALLMODE property as reference.

Answer 2

This worked for me:

<MajorUpgrade Schedule="afterInstallInitialize" AllowDowngrades="yes"  />

See WIX docs on MajorUpgrade Element.