Fun With AU Validation Tool...
The fix is quite easy, for those new to OSX or just not familiar with it. Open Applications/Utilities/Disc Utility, highlight your main drive in the left hand panel, then hit the button labeled "Repair disk permissions." After a minute or two of grinding, you're good to go. Or so it would seem.
Logic, unlike the other large AU hosts Live and Digital Performer, caches AudioUnit effects. The reasoning behind this is not entirely clear to us. However, the result is. When you add a new AudioUnit, Logic tests it with AU Validator, and if it passes, it imports the AU to its own folders and uses that version rather than the one in your Library/Audio/Plugins/Components folder. It will continue to use that version until it sees one in the Components folder that has a higher version number than the one it has cached. So if you installed Dubstation 1.0.0, then re-installed it, nothing would change in Logic. But if you installed 1.0.1, Logic would flush its cache, test the new one, and either use it, or fail Dubstation altogether if it didn't pass. For what it's worth, it doesn't make any sense to us, either.
Long story short, as a result of this caching "feature" of Logic, sometimes when you repair permissions, a plugin still won't work, because it has the same version number; even if you re-install it, it won't have any effect, because Logic didn't flush its cache because the version number was the same. There is a simple solution to this issue, though.
Open Logic Pro->Preferences->Start Logic AU Manager. This, despite the name, is basically a UI front-end for the terminal program AU Validation Tool. When you do this, Logic has to quit, so make sure your project is saved, blah, blah, blah. When you've clicked through, you're rewarded with this stuff:
Now, note the "RESCAN" buttons on the right. When a plugin isn't working in Logic, it will be greyed out here. After you do your "Repair disk permissions" operation, this will still be greyed out. Whack that "RESCAN" button for the plugin that isn't working, and a terminal window pops up with the AU Validation Tool results. Chances are, the plugin will now work, and will no longer be greyed out. As soon as you quit Logic AU Manager, Logic will re-start, and you're good to go. If this isn't the case, copy the text from that window and include it in your "what the fuck?" email to the plugin manufacturer, because they can tell a lot about your system, versions, and what is going wrong from that text.
And one more thing. You'll note that I said that Logic AU Manager was a front-end for the terminal program AU Validation Tool. You can run the AU Validation Tool by itself, without even starting Logic. This may be handy if you're a developer (in which case you probably already know this) or you're troubleshooting a plugin, or whatever.
To do all this, open up a terminal window. There are many commands you can use to view and test your AudioUnit plugins with the command line; I'll give you a couple of the most useful ones. Just type these in a terminal window as they appear, and they'll drive AU Validation Tool without any fuss nor muss:
auval -a This lists your AudioUnits, and shows some information about them. You'll need to know the four-letter/digit tags associated, so you'll need to use this. You can see in the image above that there are three four-character tags associated with each effect. Looking at Reverence, you'll note that it says "aufx ADRe AuDa" before the company and plugin name. "aufx" is the type of plugin. "ADRe" is the four-character ID code we register with Apple for the plugin, and "AuDa" is our company code.
auval -h This brings up the help file; spend some time with this, as there are a _lot_ of command line options with AUval; it is quite a handy tool.
auval -v TYPE SUBT MANU In this case, substitute "TYPE SUBT MANU" for the 12-character code you got with the -a command above, and AU Valitation Tool will run the validation for that plugin. So, to run the validation for Reverence, I would type:
auval -v aufx ADRe AuDa
The Validation Tool would then perform the full validation, just as if it was initiated from Logic AU Manager. This is especially handy for developers, but useful to all users if you're not sure why a plugin isn't working.
Anyways, that's the gist of it. There are many, many more options with AU Validation Tool, and any power user would benefit from spending some time fooling with it.