The Flash uploader has been replaced with a JS one. You only need to make sure you haven't missed the /js folder in the upgrade, and add this to your layout file
Layout file url :/app/design/adminhtml/default/default/layout/aijko/widgetimagechooser.xml
<reference name="head">
<action method="addJs"><file>lib/uploader/flow.min.js</file></action>
<action method="addJs"><file>lib/uploader/fusty-flow.js</file></action>
<action method="addJs"><file>lib/uploader/fusty-flow-factory.js</file></action>
<action method="addJs"><file>mage/adminhtml/uploader/instance.js</file></action>
</reference>
