Hmmm. Thank you, you've pointed out a coding bug on our part. JFBConnect is having an issues with storing some configuration settings in your database, which is not normal (and why this error has not been exposed sooner).
If you can change the following line, that will not throw the error. However, there's a different underlying issue with your site since I don't think your configuration settings will actually be saved. Please change the line, and if you still have issues, please message me a super admin account for your site so we can get into debug what could be going wrong.
/administrator/components/com_jfbconnect/models/config.php, change line 172 to:
$this->setError($this->_db->getErrorMsg());
Finally, did you upgrade to 2.6, or was this a clean installation?