Port Registration Error

I am running Ardour 5.12 on Ubuntu Studio 16.04. Recently I have been getting a Port Registration Error, with the message “unable to create port: failed constructor” whenever I try to open previous sessions. I found that I could open the session if I click the button “Safe Mode: Disable all Plugins”. If I save the session, close it, and try to reopen it, I get the error. I cannot open any sessions. If I close Ardour and reopen it in Safe Mode, the sessions will open successfully. How can I fix this? Thanks.

BTW, I am using only Calf Plugins

I am guessing you are using the Jack backend? There is a setting in jack that tells it the max number of ports it can create:

How to set this depends on what you are using to start Jack?

         Seablade

@seablade I am using the jack backend. I use Ardour to start Jack. My setup basically uses default settings. I don’t go into Jack very often, and I have not gone in or changed anything recently.

I did launch Ardour from the terminal. I found that I could successfully open one or two sessions, then I got the error message. On the terminal I saw “Failed to register port “Click/audio_out 1”, reason unknown from here.” I looked at one of the sessions that opened successfully, and could not see anything that looked to me (an inexperienced user) that looked out of sorts. Any thoughts?

BTW, I found that I could successfully open sessions with plugins working if I close Ardour then reopen it.

I think I fixed it. I uninstalled Ardour (including deletion of the ~/.config/Ardour5 directory), then reinstalled Ardour5 from scratch. I still had the same problem opening sessions sequentially, so I deleted the instant.xml files from several sessions and from the ~/.config/Ardour5 directory. That seemed to fix it. Looking back, the instant.xml files may have been the problem, even though I could not see any reference to Click or audio_out in them.

Hi
After reading this I removed the instant.xml and mixbus fired up fine. Cheers