What is the image your trying to import is that "VMware-VMvisor-Installer-5.0.0-469512.x86_64"?..
Make sure you import the above ISO and the disk to which you import has enough space. Even if the image has a failed the integrity also the import will fail.
if you try to upload lower version of ISO also it will fail. Download a new ISO image of vsphere 5 and try to upload, it will work.
Also a alternative.
Login to vCenter go to Home--Solutions and Applications--Update Manager--Configuration Tab--Patch Download Settings--Click on the hyperlink that says "Import Patches". It will automatically download all teh available patches and image for the vsphere5. once done. create a baseline with the image to upgrade.