error after updating to 7.2.6

When you *enable* the JFBCSystem plugin, the errors go away? If so, then I don't think there's really an issue here as the JFBCSystem plugin is supposed to always be enabled.

If you meant disable, then do or let me know the following:
* Go to the JFBConnect -> Profiles area in the admin section. Hit the 'Save' button (even if you don't change any settings). That sometimes fixes a similar PHP notice.
* Let me know the full error message you see. Usually, there will be a file name to go along with the message so we can see where the error is coming from. Please send the whole error message (you can remove path info on your server).

Thanks,
Alex