A couple of people have stumbled across the problem of not being able to install AIR applications that were written for beta 1 once they’ve installed beta 2 of the runtime.
Rather than uninstalling beta 1 of AIR before installing beta 2, leave beta 1 installed and beta 2 will be installed alongside the previous version of the runtime. This enables applications written for both beta 1 and beta 2 to be installed and run.
You can download both the beta 1 and beta 2 runtimes from Adobe Labs. If you’ve already installed beta 2 and need to run applications not yet updated for the new runtime, then uninstall beta 2, re-install beta 1 first and then install beta 2.
Check the AIR release notes for further information, especially if you want to run beta 1 and beta 2 side-by-side on Windows (there can be issues due to account security privileges).