It's the setting of your error_reporting(). Check the php.ini file to see how high this is set, or just put error_reporting(0); at the top of all of your scripts. Choose a different value than 0 though, you still want to know when the system crashes, and what for.
Or go through all of your code and initialize any variables that you are using before initializing. This is the proper way to do things since it will make your code more portable, and have less surprises.
Typically I get these when I do something in a loop where I'm adding to a string varible and using the .= operater, but haven't declared the variable first. It's easy to just put the variable = "" outside the loop and get rid of the error.
