I was unable to reproduce this issue on my own system. I successfully downloaded the files for all four iTunes 11.1 packages.
Have you recently downloaded files for another iTunes package?
The files are generically named (i.e. iTunesSetup.exe and iTunes64Setup.exe). Is it possible that the Patch Manager server downloaded cached files from a proxy server?
Navigate to the package folders on the Patch Manager server and verify that the File Version for those files is actually 18.104.22.168.
C:\Program Files\SolarWinds\Patch Manager\Server\packages\publisher\422c495c-32da-4ddf-bc0a-49c1092ec058\iTunes64Setup.exe
C:\Program Files\SolarWinds\Patch Manager\Server\packages\publisher\d4ae88d5-405d-4e71-aba2-6eb29650bdcd\iTunesSetup.exe
The only iTunes packages I have downloaded were the 22.214.171.124 (x86 & x64) Upgrades from 8/20/2013, which deployed successfully.
I then downloaded the content for the 126.96.36.199 (x86 & x64) Upgrades today and had that message.
We don't use any proxy servers, just direct connect.
I didn't have those package folders on my server . . . What should I try next?
Before I went to apply the hotfix, I restarted the Patch Manager and tried it again and it worked successfully, i'll keep the hotfix handy in case this should happen in the future!