How to backtrace PHP errors in the log??

Hi
I am getting the following errors in the Drupal log,they are from a googlebot, I am getting about 5 per minute and I want to find out what is causing them, quite new to Drupal and PHP so any help is greatly appreciated.


Type php
Date Thursday, February 16, 2012 - 20:36
User Anonymous (not verified)
Location http://www.speech-therapy.org.uk/biblio?page=2&f%5Bauthor%5D=91&f%5Bag%5D=L&s=type&o=asc
Referrer
Message Notice: Trying to get property of non-object in eval() (line 3 of /home/sltruweb/public_html/modules/php/php.module(80) : eval()'d code).
Severity notice
Hostname 66.249.72.23
Operations