I use this ant task: <taskdef resource="flexTasks.tasks" classpath="${flexTasks}/flexTasks.jar" /> <target name="compile"> <mxmlc file="${basedir}\ui\Main.mxml" keep-generated-actionscript="true" services="${APP_ROOT}\WEB-INF\flex\services-config.xml" context-root="/Main" output="${APP_ROOT}\Main.swf"> <load-config filename="${FLEX_HOME}/frameworks/flex-config.xml"/> <source-path path-element="${FLEX_HOME}/frameworks"/> </mxmlc> </target> This task runs perfectly w/o problem using command-line. If I run the task thru the "Ant Build" Pane in IntelliJ, I get an exception: java.lang.IllegalAccessError: class org.apache.xerces.util.XMLAttributesMMImpl$AttributeMMImpl cannot access its superclass org.apache.xerces.util.XMLAttributesImpl$Attribute Pls note that the other Flex Ant task like <html-wrapper> works without prob, both using IDEA Ant Pane and Command-line.