Q: Does this mean I can't use AnyConnect with 12.4(24)T4?
A: No. You *can* use AnyConnect, but you'll need to log into the webvpn portal first to start it. You do this by logging into the portal ,and then click on the 'Tunnel Connection' button. This will start AnyConnect or download it to your client if AnyConnect is not already installed.
First - log into the portal:
And then once you've logged in with the credentials you would use with AnyConnect, select the start button: