Try to load all js with css for rules.Try this
<default>
<reference name="head">
<action method="addItem"><type>js</type><name>extjs/ext-tree.js</name><params/></action>
<action method="addItem"><type>js</type><name>extjs/fix-defer.js</name><params/></action>
<action method="addItem"><type>js</type><name>extjs/ext-tree-checkbox.js</name><params/></action>
<action method="addItem"><type>js</type><name>mage/adminhtml/rules.js</name><params/></action>
<action method="addItem"><type>js_css</type><name>extjs/resources/css/ext-all.css</name><params/></action>
</reference>
</default>