[Plugin: Bit.ly Shortlinks] PHP error

The bit.ly link was created, but this message was displayed on my page:

Warning: Header may not contain more than a single header, new line detected. in /home/…/wp-includes/link-template.php on line 2435

Also, the Admin header/ribbon was up, down, up, down alternating. I verified that once I took out the plugin’s wp-config.php settings, everything went back to normal.