Headers already sent issue

I spent several hours tracing this issue down. Headers already sent… What happened was some bogus (invisible) characters were getting inserted at the beginning of any php file I edited. I validated the home page using WP’s valid XHTML. Sure enough, invalid characters appeared in column 0, line 1. I used “PHP Designer 2007” editor by MP Software because it was the only one (that I had) that showed the bogus characters. wp-config.php had them as well as several in the template I was using (footer.php, sidebar.php, etc). Hope this helps!
Doug