Your /RadControls/Editor/ConfigFile.xml file is probably missing the image property values. Open that file up and make sure the image areas look something like this:
Code:
<property name="ImagesPaths">
<item>~/images</item>
</property>
<property name="UploadImagesPaths">
<item>~/images</item>
</property>
<property name="DeleteImagesPaths">
<item>~/images</item>
</property>
<property name="ImagesFilters">
<item>*.gif</item>
<item>*.jpg</item>
<item>*.jpeg</item>
<item>*.png</item>
<item>*.bmp</item>
</property>