I'm using MT-PowerDrumKit and I've sent the snare to a separate output. I have reverb on the snare but I want to boost the reverb for a few bars, so I add an FX automation envelope but as soon I select the parameter for the envelope, I get this error - "An error occurred while processing the undo buffer', ' A necessary COM interface was not available.'

Can anyone shed any light on this? Is it a bug? I can add FX envelopes to normal tracks, but not to the buss. And I've tried several reverbs and other effects, different projects and different drum plugins, nothing works.

Acid Pro 8, Windows 10.