see this thread for details on troubleshooting the headers already sent error:
http://www.webassist.com/forums/posts.php?id=19285
in your case, it is the BOM Signature bug causing the problem:
2) The Unicode Signature (BOM) PHP bug. the forth screen shot shows the Title / Encoding category of the Page Properties screen (Modify - > Page Properties). Checking the Include Signature (BOM) option can cause the headers already sent error 


