The Adobe Exchange Download page has an old version of Adobe Extension Manager that fails on Mac OS Mountain Lion and later. Anyone who attempts to download Extension Manager gets this old version, 22.214.171.124.
Version 5.5.3 is available from the following link, but Adobe search and download page link to the exchange download, not this link.
Adobe, Please update the link so that we can a little more easily download a version that doesn't show the misleading error "The Extension does not contain a valid signature. The extension will not be installed".
Sorry for that. We listed the old version in that page because the latest 5.5.3 patch can be installed ONLY AFTER you have installed the old version. Actually you can find the product updates at http://www.adobe.com/downloads/updates/. Also you can launch Adobe Application Manager or Creative Cloud app to learn which products are updatable and update them if necessary.