This might be due to the Uploader module not being recognized. Try flushing your configuration cache (System > Cache Management or rm -rf var/cache/*).

This might be due to the Uploader module not being recognized. Try flushing your configuration cache (System > Cache Management or rm -rf var/cache/*).

Make sure following files are in place and readable by the webserver – try retrieving their URLs directly to see if this is the case:

js/lib/uploader/flow.min.js
js/lib/uploader/fusty-flow-factory.js
js/lib/uploader/fusty-flow.js
js/mage/adminhtml/uploader/instance.js

Ensure file app/design/adminhtml/default/default/layout/main.xml contains

<action method="addJs"><name>lib/uploader/flow.min.js</name></action>
<action method="addJs"><name>lib/uploader/fusty-flow.js</name></action>
<action method="addJs"><name>lib/uploader/fusty-flow-factory.js</name></action>
<action method="addJs"><name>mage/adminhtml/uploader/instance.js</name></action>

If this is the case, flush your layout cache and especially delete your merged JS & CSS file cache (lower left at System > Cache Management).