The install of application "application name" from policy "policy name" failed. The error was : The installation source for this product is not available. Verify that the source exists and that you can access it.
This message is most common when assigning software packages to computers in a domain, and the usual cause are incorrect permission on the installation package folder.
Check the share and the NTFS permissions to make sure that everyone (or another group that the computer/users are members of) has at least read permission.