Need help with Webm

when i download webm from fnordware it does not show up in my encoder at all but if i use the extension via adobe it shows up but since it's not the latest version "include alpha channel" is not available. i have literally been trying to figure this out for hours and have tried everything i possibly can. i've uninstalled webm, Ae, Me...went to older versions...reinstalled...everything i try has had the same outcome.