Fbkey error, how to fix!

Hi, I get this error permanently on my site, even though I have the plugin and wordpress updated to date. I only use the sharing (with counter) and commenting modalities, and although I have read that this is just a warning, it is quite annoying as it generates about 20 alerts every 10 minutes, making the error_log file grow quite quickly; thanks if anyone can help.

PHP Warning: Undefined array key “fb_key” in …super-socializer/inc/social_sharing.php on line 296