Intermittent "No such file" message

I have a baffling situation occurring on a web server running IIS (Windows Server 2003). There is one particular page which sometimes generates errors trying to execute a particular 'require' statement. The file which is being included contains a simple banner and is included at the head of every page on our site. Yet the 'require' statement sometimes fails with this message: Error in D:\inetpub\wwwroot\conferences\default.php On line 12, error #2, in D:\inetpub\wwwroot\conferences\default.php: "require(../apr03ban.html) [<a href='function.require'>function.require</a>]: failed to open stream: No such file or directory" The error always occurs in this file, default.php, and not in any other. Further, analysis of the errors reveals the following pattern. In every case, one of the following is true: A) The user agent contains one of the following patterns: Googlebot/2.1; +http://www.google.com/bot.html Yahoo! Slurp; http://help.yahoo.com/help/us/ysearch/slurp msnbot/1.0 (+http://search.msn.com/msnbot.htm) CazoodleBot Crawler; http://www.cazoodle.com/cazoodlebot psbot/0.1 (+http://www.picsearch.com/bot.html) or, B) The referrer looks like one of these: http://search.msn.com/results.aspx?q=seton+homeschool&FORM=MSNH http://search.msn.com/results.asp?FORM=sCPN&RS=CHECKED&un=doc&v=1&q=homeschool%20conference http://search.live.com/results.aspx?q=catholic+homeschooling&first=11&FORM=PERE As you can see, there is a definite pattern here. The error is not occuring purely at random. However, this brings me no closer to a solution. Does anyone have any ideas for possible explanations, or for what kinds of tests I could do to track down the cause of the problem? Thanks. -- Thank you, Lewis Kapell Computer Operations Seton Home Study School