I have ezdrummer and ezkeys, both are installed (including AU) and authorized but still won’t show up in garageband. Other plugins all appear just fine. I have followed the steps to force garageband to rescan AUs, which worked to do the rescan but still no toontrack plugins show up. I found a thread here on the forum but that didn’t offer much other than to confirm AU support is installed (it is) and to try rebooting.
edit: finally figured it out, was clicking on the fx plugins and not the instrument plug-in section under plug-ins, not even realizing they were different or separate.
