When you try to install an update for an Adobe CS5 product, the Adobe Application Manager indicates, "Some updates failed to install." Then, below the name of one or more of the updates you were attempting to install, the message indicates, "Update is not applicable."
If you are attempting to install an update for an application that is not installed, this message is expected. Ignore it and don't install the update again. Otherwise, install the desired software, then run the update again.
If you have a prerelease build of an Adobe product, this message occurs. In this situation, uninstall the current version, and install from a source known to be the final build released by Adobe.
If neither of these situations appear to be the case for your system, or if your update fails with the message, "Installation failed," try searching the knowledgebase. The knowledgebase contains information for known issues specific to the particular update you are attempting to install. If no match is found, try using the knowledgebase article, Troubleshoot CS5 installation with install logs (cpsid_84451).