If you are receiving an error message starting with "Notice", for example:
Notice: Undefined index in xy.php at line 123.
this is not an error, it is just a message, which is automatically processed correctly by php, so it can't make a problem. It is written out for you, because the highest error reporting is turned on at your website. Of course, please contact us, when you see something like this pointing to one of our files, but if you don't see any other "Warning" or "Fatal error" messages, then this can't cause you any trouble, so you don't have to worry about it.