JFBConnect conflict error with Powermail

Actually, the issue is likely in what powermail is doing in that file at line 73. If they are echoing out data or doing something that would start the output of the HTML at that stage, which they shouldn't, it would be causing the warning message you show. JFBConnect is trying to set a cookie in the browser. That has to be done before any content is passed back to the user. Joomla normally doesn't send anything to the user until everything has executed, but some extensions try to send data 'outside' of the normal Joomla method. In this case, our cookie wouldn't be sent and you'd see that warning.

One way to possibly mask (and maybe fix) the problem is to simply set the Error Reporting setting in the Joomla -> Global Configuration area to 'None'. That will prevent the warning from showing, but the underlying (possibly) bad behavior in powermail may still be present and cause issues with the cookie we set. If you run into issues with JFBConnect, you may need to investigate line 73 of the powermail file further to determine what's happening there.

I hope that helps explain,
Alex