We are using Confluence v3.3 and were noticing a strange error: Unable to render embedded object: File (file-name) not found on Wiki pages sometimes while inserting images. I tried renaming file names and it did work sometimes but it failed some other times as well because i kept noticing such error messages on wiki pages. So, i was looking for a FIX to it.
I googled and found this http://confluence.atlassian.com/display/CONFKB/Seeing+%27unable+to+render+embedded+object%27+Error+for+Images+from+Certain+Pages where Atlassian has shared that it's a Known Issue because of a feature CamelCase Links in Confluence. So, disable this feature and it would fix the issue for you.
To disable/enable CamelCase Links feature in Confluence, you can check http://confluence.atlassian.com/display/DOC/Enabling+CamelCase+Linking. It helped us and i hope it would be useful for others too so, thought to share it. :)