To debug a VoiceAttack plugin, there are few things you'll need to do. First, you'll need to make sure that the plugin outputs the .dll into VoiceAttack's folder structure. That means that the plugin dll needs to go into VA's Apps folder within a subfolder:
C:\Program Files (x86)\VoiceAttack\Apps\MyPluginFolder
You get the dll into that folder by going into the plugin's project settings, down to the Build tab and setting this in the Output path box.
Build the plugin once so that the dll appears in that folder. You may have to adjust security settings depending on your machine. To do that, just right click on the new folder you created in the Apps folder, select, 'properties' then 'security' and set All Users (or whatever) to 'Full Control' (or however you want to set up your own security settings).
Open VA, turn on plugin support (restart VA). Open the plugin manager and select the new plugin you just built.
Next, open the plugin's project settings, go down to the Debug tab and set the, 'Start external program' value to the path of VA (usually C:\Program Files (x86)\VoiceAttack\VoiceAttack.exe).
Set a breakpoint somewhere like in the init or displayname functions so you can see things happening.
You can now just, 'run' the plugin project. VA will be launched and then the plugin's display or init will be run (cant remember which is first).
I'll need to update the VA documentation to reflect this, as it makes the horrible assumption that if you're down this far in the weeds you've probably done this before. Again - horrible assumption