Unexpected failure: null when packaging iOS app

I'm trying to package an iOS app and getting the following error message:

adt.bat -package -target ipa-app-store -keystore ios_prod.p12 -storetype pkcs12 -storepass xxxxxxxxx -provisioning-profile ios_prod.mobileprovision output.ipa ipa.xml game.swf icons

unexpected failure: null

java.io.IOException

        at com.adobe.air.ipa.IPAOutputStream$CompileTask.throwAppropriateException(IPAOutputStream.java:1219)

        at com.adobe.air.ipa.IPAOutputStream.finalizeSig(IPAOutputStream.java:1467)

        at com.adobe.air.ApplicationPackager.createPackage(ApplicationPackager.java:227)

        at com.adobe.air.ipa.IPAPackager.createPackage(IPAPackager.java:291)

        at com.adobe.air.ADT.parseArgsAndGo(ADT.java:673)

        at com.adobe.air.ADT.run(ADT.java:471)

        at com.adobe.air.ADT.main(ADT.java:521)

This is the ipa.xml content:

<?xml version="1.0" encoding="UTF-8"?>

<application xmlns="http://ns.adobe.com/air/application/27.0">

    <id>com.xxxxx.xxxxx</id>

    <name>XXXXX XXXXX</name>

    <versionNumber>0.1.0</versionNumber>

    <filename>XXXXXX</filename>

    <supportedProfiles>mobileDevice extendedDesktop</supportedProfiles>

<supportedLanguages>en</supportedLanguages>

    <customUpdateUI>false</customUpdateUI>

    <allowBrowserInvocation>false</allowBrowserInvocation>

    <initialWindow>

        <content>game.swf</content>

        <fullScreen>true</fullScreen>

        <aspectRatio>portrait</aspectRatio><!-- portrait -->

        <autoOrients>false</autoOrients>

        <visible>true</visible>

        <renderMode>direct</renderMode>

        <depthAndStencil>true</depthAndStencil>

        <resizable>false</resizable>

    </initialWindow>

    <icon>

        <image29x29>icons/icon29.png</image29x29>

        <image57x57>icons/icon57.png</image57x57>

        <image72x72>icons/icon72.png</image72x72>

        <image76x76>icons/icon76.png</image76x76>

        <image114x114>icons/icon114.png</image114x114>

        <image120x120>icons/icon120.png</image120x120>

        <image152x152>icons/icon152.png</image152x152>

        <image512x512>icons/icon512.png</image512x512>

    </icon>

</application>

Any idea ?