In my ant build.xml script I have...

  <namespace uri="http://ns.foo.com/mxml/2011" manifest="src/manifest.xml"/>
  <namespace uri="library://ns.adobe.com/flex/spark" manifest="flex_src/spark-manifest.xml"/>
  <namespace uri="http://www.adobe.com/2006/mxml" manifest="flex_src/mx-manifest.xml"/>

That works! But... I'm not sure how to add these namespaces to my project properties in Flash Builder 4 so I can debug. When I try, it changes this line in my .actionScriptProperties

<compiler additionalCompilerArguments="-namespace http://ns.foo.com/mxml/2011 src/manifest.xml -namespace=library://ns.adobe.com/flex/spark flex_src/spark-manifest.xml -namespace http://www.adobe.com/2006/mxml flex_src/mx-manifest.xml" autoRSLOrdering="true" copyDependentFiles="true" fteInMXComponents="false" generateAccessible="true" htmlExpressInstall="true" htmlGenerate="false" htmlHistoryManagement="false" htmlPlayerVersionCheck="true" includeNetmonSwc="false" outputFolderPath="bin-debug" sourceFolderPath="src" strict="true" targetPlayerVersion="0.0.0" useApolloConfig="true" useDebugRSLSwfs="true" verifyDigests="true" warn="true">

but gives me a "no default arguments are expected" error.

What is the reason for this error? The error location is "Unknown" and seems to refer to these compiler arguments.