WiX ComboBox Element is not valid in XML Schema

I'm trying to add dialog for IIS settings. I wanted to have a ComboBox with Identities, so that users can choose either from default identities or enter their own service account settings.

<?xml version="1.0" encoding="UTF-8"?>
<Wix xmlns="http://ift.tt/1cKQ1oM">
    <Fragment>
    <UI>
      <Dialog Id="IISDialog" Width="370" Height="270">
        <Control Type="Edit" Id="IISDomain" Width="329" Height="15" X="22" Y="135" Property="WEB_APP_POOL_IDENTITY_DOMAIN"/>
        <Control Type="Text" Id="IISDomainLabel" Width="152" Height="10" X="22" Y="120">
          <Text>Account Domain:</Text>
        </Control>
        <Control Type="GroupBox" Id="CustomCredentials" Width="352" Height="128" X="10" Y="102">
          <Text>Custom Credentials</Text>
        </Control>
        <Control Type="Edit" Id="IISUser" Width="329" Height="15" X="22" Y="169" Property="WEB_APP_POOL_IDENTITY_USER">
          <Condition Action="enable">
            <![CDATA[IsUseCustomAccount]]>
          </Condition>
          <Condition Action="disable">
            <![CDATA[IsUseCustomAccount]]>
          </Condition>
        </Control>
        <Control Type="Text" Id="IISUserLabel" Width="323" Height="13" X="22" Y="154">
          <Text>User:</Text>
        </Control>
        <Control Type="MaskedEdit" Id="IISPWD" Width="328" Height="15" X="22" Y="206" Property="WEB_APP_POOL_IDENTITY_PASSWORD">
        </Control>
        <Control Type="Text" Id="IISPWDLabel" Width="50" Height="10" X="22" Y="191">
          <Text>Password:</Text>
        </Control>
        <Control Type="ComboBox" Property="DefaultAccount_Prop" Id="DefaultAccount" Width="104" Height="16" X="11" Y="49">
          <Condition Action="enable">
            <![CDATA[IsUseCustomAccount]]>
          </Condition>
          <Condition Action="disable">
            <![CDATA[IsUseCustomAccount]]>
          </Condition>
          <ComboBox Property="DefaultAccount_Prop">
            <ListItem Text="1" Value="1"/>
            <ListItem Text="2" Value="2"/>
          </ComboBox>
        </Control>
        <Control Type="CheckBox" Id="IsCustomAccount" Width="346" Height="17" X="11" Y="75" Property="IsUseCustomAccount" CheckBoxValue="1">
          <Text>Use Custom Account</Text>
        </Control>
        <Control Type="Text" Id="DefaultAccLabel" Width="105" Height="12" X="11" Y="30">
          <Text>System accounts:</Text>
        </Control>
        <Control Type="PushButton" Id="OK" Width="56" Height="17" X="304" Y="244">
          <Text>Next</Text>
        </Control>
        <Control Type="PushButton" Id="Back" Width="56" Height="17" X="244" Y="244">
          <Text>Back</Text>
        </Control>
      </Dialog>
    </UI>
    </Fragment>
</Wix>

But when I try to compile I get the following error:

error CNDL0107 : Schema validation failed with the following error at line 1, column 2731: The element 'Control' in namespace 'http://ift.tt/1cKQ1oM' has invalid child element 'ComboBox' in namespace 'http://ift.tt/1uXZ2Gh /2006/wi'. List of possible elements expected: 'Condition Publish Subscribe'. []

Any idea why this could happen? Btw when I try to get suggest from Intellisense, it also doesnt recognize combobox element. WiX version Im using is 3.9