Auto actions email with CB Subs plan information

When I enable Content Plugins, it gives:
"string(99) ":: Action 41 :: Email failed to send. Error: You must provide at least one recipient email address." string(99) ":: Action 41 :: Email failed to send. Error: You must provide at least one recipient email address."

When I disable content plugins, there is no error and the email is sent as expected, minus req'd substiutions. The email is set to send to a fixed email address as specified in the auto action, so I'm not sure why it would give this error when content plugins is enabled.

That's a conflict with CB Content Bot probably. Install latest CB 2.x nightly. Next install CB Content Bot 4.0.1. Finally install latest CB Auto Actions nightly. It should solve the issue.

CB 2.x Nightly:
www.joomlapolis.com/downloads/doc_details/640-community-builder-nightly-build

CB Content Bot 4.0.1:
www.joomlapolis.com/downloads/doc_details/842-cb-content-bot-401

CB Auto Actions Nightly:
www.joomlapolis.com/downloads/doc_details/669-cb-auto-actions-nightly-release

After installing the latest CB nightly the site went down completely (Error 500 front end and back end). There were no errors reported in php but I didn't have error logging turned on in Joomla and couldn't access the back end to enable it. I tried some basic troubleshooting (looked through .htaccess for obvious problems) but in the end I couldn't afford any more down time and had to roll back to the last backup to restore it. I haven't had the courage to try again...
I think I'll find another way using CB Subs Mailer via a cron job instead until the next stable release.

Don't see how latest nightly could crippled your install. We're using it here on Joomlapolis and on several test installs fine. It's possible you've an out of date CB plugin that could be loading and causing problems or you hit php memory limit during install and caused the install to be interrupted and break.

Please check server error log to see if any fatal errors are reported there in detail.

I think I'll find another way using CB Subs Mailer via a cron job instead until the next stable release.

That's not going to matter. As explained our nightlies are more stable than stable and go through the same review and testing process.

I called my web host for help after the site went down and they could see any errors reported. The CB update actually completed through to success status in Joomla. Then when I went to continue to use the site (backend) it was unresponsive. I then checked the front end and it was the same.

The site is particularly busy at the moment (most members pay leading up to the end of financial year), but I will try again at the start of July and report back.
Thanks for you help to-date.

I recommend not directly updating a live site, but first testing updates on a clone of your live site. Basically a staging area so you know what to expect (it's the process we do here in fact to minimize problems).