<--This issue drove me nuts this week. Someone uploaded a bunch of ISO images with vCloud Director 5.5. The ISO's images uploaded fine but some images appeared as normal and others appeared as icons with a question mark that are unmountable on VM's. WTF?
So I tried a couple things. I noticed that the ISO images were missing the .iso file extension. I tried renaming the ISO images through vCloud. No Love!
How to fix Unknown ISO files in vCloud
In order to fix this annoying issue ensure your ISO images have the .iso extension before uploading. vCloud 5.1 and lower this was not an issue and vCloud automatically recognized the file type. Now we must tell it before the upload.