Replace Plugin throws error

I’ve been away from music software for almost two years, but now I’m updating the entirely way too many apps and plugins that I own and stumbled on a bug when going through and registering new plugin upgrades. I typically use Cantabile to do that because it’s easier to load and replace my way through them all instead of using a DAW.

The bug is that when I right-click a loaded plugin, and then click “Replace Plugin…”, I get a error popup saying “Error replacing plugin - Object reference not set to an instance of an object.”. That happens before the plugin dialog should appear.

Cantabile 4.0.4176 x64


Hi @Fesick,

Thanks for reporting this. I’ve had a couple of reports of this but haven’t been able to reproduce it.

Couple of question:

  1. What plugin are you replacing (name and VST 2 or 3)
  2. Does this happen if you load a new instance of the plugin in a new song and then try to replace it, or only with an instance loaded from an old song.


I’m not 100% sure but I think this error pops up whenever you are replacing a VST2 with a VST3 plugin.

It happens with every plugin that I try it with. I just tested both the VST2 and VST3 versions of the same plugin with the same results. It’s in a new default song when opening up Cantabile.

Here is a screenshot of the console log:

Another thing to note is that it is a fresh install of Cantabile. I had uninstalled v3 and v4, wiped out the AppData/Local folder and the installed only v4.

Let me know if there is anything else I can do to help track it down.

EDIT: I also relocate all folders and the background rack from the default locations.


For me, it happens before I can even choose a replacement plugin. It’s immediately after I click “Replace Plugin…”.


Can I get you to send me some log files:

  1. Start Cantabile
  2. From the Tools menu, choose Open Settings Folder
  3. Reproduce the problem
  4. Close Cantabile (this is important).

From the folder opened in step 2, send me the files settings.json, plugins.json, log.txt and log-previous.txt and I’ll check it out.

Also can you confirm this happens for Replace Plugin, but not Insert Plugin?


I will get those files to you shortly.

Replace Plugin has always resulted in the error every time I attempt it. I can insert plugins all day long just fine. I can also delete them, then insert new ones.

I just noticed that if I set the plugin to the “Unloaded” state, I can then Replace Plugin. It throws the error from either “Running” or “Suspended” states. I get the same results from within an embedded rack.

I tried changing to a different audio device and that didn’t help. I’ll experiment some more after I send you the files.


I believe the issue has to do with changing the Insert Plugin dialog Default Group to “By Folder”. When I change it back to “All Plugins”, Replace Plugin works as expected.


Thanks to @Fesick great work narrowing this down, I’ve now reproduced it and a fix will be in the next build.