I found that if I were to simply copy the files to directories in the Portals/_default/Skins and Portals/_default/Containers directories, that I could select the skins and containers and that all was just fine.
From that, I conclude that there is something in your manifest file that needs to be changed. I haven't figured out what it is, though.
My suggestion is that you read
this blog entry, and follow Timo's advice. First, package up your skins and containers in the old style format, and install the skin. You can then use the tools in DotNetNuke to package the skins and containers in the new format, letting DotNetNuke build the manifest files.
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I did that, and was able to install the newly packaged skin correctly. Oddly, I really cannot see any difference between the manifest file in your skin and the one that DotNetNuke generated for me. I'm completely baffled.
But, it does work.