das liegt wohl an Deiner Flexform, die ist nicht korrekt.
Anbei einmal die Flexform des neuen MediaCEs da die auch sections enthält. Vergleiche es mal!
Code:
<?xml version="1.0" encoding="utf-8"?>
<T3DataStructure>
<meta>
<langDisable>1</langDisable>
</meta>
<sheets>
<sDEF>
<ROOT>
<TCEforms>
<sheetTitle>LLL:EXT:cms/locallang_ttc.xml:media.options</sheetTitle>
</TCEforms>
<type>array</type>
<el>
<mmFile>
<TCEforms>
<label>LLL:EXT:cms/locallang_ttc.xml:media.url</label>
<config>
<type>input</type>
<size>60</size>
<eval>trim</eval>
<default></default>
<wizards type="array">
<_PADDING>2</_PADDING>
<link type="array">
<type>popup</type>
<title>LLL:EXT:cms/locallang_ttc.xml:media.browseUrlTitle</title>
<icon>link_popup.gif</icon>
<script>browse_links.php?mode=wizard&act=file|url</script>
<params type="array">
<blindLinkOptions>page,folder,mail,spec</blindLinkOptions>
<allowedExtensions>class,swf,swa,dcr,wav,avi,au,mov,asf,mpg,wmv,mp3,mp4,m4v,flv</allowedExtensions>
</params>
<JSopenParams>height=300,width=500,status=0,menubar=0,scrollbars=1</JSopenParams>
</link>
</wizards>
</config>
</TCEforms>
</mmFile>
<mmforcePlayer>
<TCEforms>
<label>LLL:EXT:cms/locallang_ttc.xml:media.forcePlayer</label>
<config>
<type>check</type>
<default>1</default>
</config>
</TCEforms>
</mmforcePlayer>
<mmType>
<TCEforms>
<label>LLL:EXT:cms/locallang_ttc.xml:media.type</label>
<config>
<type>select</type>
<items>
<numIndex index="0">
<numIndex index="0">LLL:EXT:cms/locallang_ttc.xml:media.type.video</numIndex>
<numIndex index="1">video</numIndex>
</numIndex>
<numIndex index="1">
<numIndex index="0">LLL:EXT:cms/locallang_ttc.xml:media.type.audio</numIndex>
<numIndex index="1">audio</numIndex>
</numIndex>
</items>
</config>
</TCEforms>
</mmType>
<mmWidth>
<TCEforms>
<label>LLL:EXT:cms/locallang_ttc.xml:media.width</label>
<config>
<type>input</type>
<size>8</size>
<max>5</max>
<eval>trim</eval>
</config>
</TCEforms>
</mmWidth>
<mmHeight>
<TCEforms>
<label>LLL:EXT:cms/locallang_ttc.xml:media.height</label>
<config>
<type>input</type>
<size>8</size>
<max>5</max>
<eval>trim</eval>
</config>
</TCEforms>
</mmHeight>
<mmRenderType>
<TCEforms>
<label>LLL:EXT:cms/locallang_ttc.xml:media.renderType</label>
<config>
<type>select</type>
<items>
<numIndex index="0">
<numIndex index="0">LLL:EXT:cms/locallang_ttc.xml:media.renderType.auto</numIndex>
<numIndex index="1">auto</numIndex>
</numIndex>
<numIndex index="1">
<numIndex index="0">LLL:EXT:cms/locallang_ttc.xml:media.renderType.swf</numIndex>
<numIndex index="1">swf</numIndex>
</numIndex>
<numIndex index="2">
<numIndex index="0">LLL:EXT:cms/locallang_ttc.xml:media.renderType.qt</numIndex>
<numIndex index="1">qt</numIndex>
</numIndex>
<numIndex index="3">
<numIndex index="0">LLL:EXT:cms/locallang_ttc.xml:media.renderType.embed</numIndex>
<numIndex index="1">embed</numIndex>
</numIndex>
</items>
<itemsProcFunc>tx_cms_mediaItems->customMediaRenderTypes</itemsProcFunc>
</config>
</TCEforms>
</mmRenderType>
<mmMediaOptions>
<tx_templavoila>
<title>LLL:EXT:cms/locallang_ttc.xml:media.additionalOptions</title>
</tx_templavoila>
<type>array</type>
<section>1</section>
<el>
<mmMediaOptionsContainer>
<type>array</type>
<tx_templavoila>
<title>LLL:EXT:cms/locallang_ttc.xml:media.params</title>
</tx_templavoila>
<el>
<mmParamName>
<TCEforms>
<label>LLL:EXT:cms/locallang_ttc.xml:media.params.option</label>
<config>
<type>select</type>
<items>
<numIndex index="0">
<numIndex index="0">LLL:EXT:cms/locallang_ttc.xml:media.params.autoPlay</numIndex>
<numIndex index="1">autoPlay</numIndex>
</numIndex>
<numIndex index="1">
<numIndex index="0">LLL:EXT:cms/locallang_ttc.xml:media.params.loop</numIndex>
<numIndex index="1">loop</numIndex>
</numIndex>
<numIndex index="2">
<numIndex index="0">LLL:EXT:cms/locallang_ttc.xml:media.params.quality</numIndex>
<numIndex index="1">quality</numIndex>
</numIndex>
<numIndex index="3">
<numIndex index="0">LLL:EXT:cms/locallang_ttc.xml:media.params.preview</numIndex>
<numIndex index="1">preview</numIndex>
</numIndex>
<numIndex index="4">
<numIndex index="0">LLL:EXT:cms/locallang_ttc.xml:media.params.allowScriptAccess</numIndex>
<numIndex index="1">allowScriptAccess</numIndex>
</numIndex>
<numIndex index="5">
<numIndex index="0">LLL:EXT:cms/locallang_ttc.xml:media.params.allowFullScreen</numIndex>
<numIndex index="1">allowFullScreen</numIndex>
</numIndex>
</items>
<itemsProcFunc>tx_cms_mediaItems->customMediaParams</itemsProcFunc>
</config>
</TCEforms>
</mmParamName>
<mmParamSet>
<TCEforms>
<label>LLL:EXT:cms/locallang_ttc.xml:media.params.setTo</label>
<config>
<type>select</type>
<items>
<numIndex index="0">
<numIndex index="0">LLL:EXT:cms/locallang_ttc.xml:media.params.on</numIndex>
<numIndex index="1">1</numIndex>
</numIndex>
<numIndex index="1">
<numIndex index="0">LLL:EXT:cms/locallang_ttc.xml:media.params.off</numIndex>
<numIndex index="1">0</numIndex>
</numIndex>
<numIndex index="2">
<numIndex index="0">LLL:EXT:cms/locallang_ttc.xml:media.params.valueEntry</numIndex>
<numIndex index="1">2</numIndex>
</numIndex>
</items>
</config>
</TCEforms>
</mmParamSet>
<mmParamValue>
<TCEforms>
<label>LLL:EXT:cms/locallang_ttc.xml:media.params.value</label>
<config>
<type>input</type>
<size>16</size>
<default></default>
</config>
</TCEforms>
</mmParamValue>
</el>
</mmMediaOptionsContainer>
<mmMediaCustomParameterContainer>
<type>array</type>
<tx_templavoila>
<title>LLL:EXT:cms/locallang_ttc.xml:media.params.customEntry</title>
</tx_templavoila>
<el>
<mmParamCustomEntry>
<TCEforms>
<label>LLL:EXT:cms/locallang_ttc.xml:media.params.customEntryLabel</label>
<config>
<type>text</type>
<rows>6</rows>
<cols>60</cols>
</config>
</TCEforms>
</mmParamCustomEntry>
</el>
</mmMediaCustomParameterContainer>
</el>
</mmMediaOptions>
</el>
</ROOT>
</sDEF>
</sheets>
</T3DataStructure>
wie Du siehst gehört bei section auch ein type=array dazu.
Line 1: Empty document deutet auf invalides xml