Re: "Unable to download, Application package not found."

My guess is that the app. manager needed an update of the listing. If the name (version number) of the package was changed / moved on the repository then the app. manager would look for the wrong (non-existing) file. So, update the listing and try again if such things happens.

(The other possibility is that the repository Packages file is inconsistent with reality, but this is rare because it tends to be generated automatically by the repository management software)