cannot send session cookie - headers already sent

I got these messages :
>>>>>>>>>>>>>>>>>>
Warning: session_start() [function.session-start]: Cannot send session cookie - headers already sent by (output started at C:\xampp\htdocs\bcef\files\mailstuff\email2.php:1) in C:\xampp\htdocs\bcef\files\mailstuff\email2.php on line 4

Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at C:\xampp\htdocs\bcef\files\mailstuff\email2.php:1) in C:\xampp\htdocs\bcef\files\mailstuff\email2.php on line 4
>>>>>>>>>>>>>>>>>>
after setting up an email form as instructed and testing it in a browser. The message means nothing to me, and neither does the explanation in the PHP manual. There is nothing about this in any of the documentation for the product. The last version never came up with any error messages, so I am totally at a loss.

Can anyone help?

the headers already sent error is ussually caused by blank space or other output between PHP code bloacks.

see the following thread for details on troubleshooting the headers already sent error.

showthread.php?t=19285

since the error is being reported at line 1, check these 2 possible causes as well:

Originally Said By: Jason Byrnes

  There are 2 other causes of the Headers already sent error besides output to the page. Look for these causes if the output is reported at line 1 in the error:
1) Using the virtual() function to include php files instead of require once:

php:

<?php virtual('Connections/connEAF.php'); ?>

In Dreamweaver's site settings panel, the Local Info tab has a settings for "Links relative To" if you select Site Root (see the third screen shot), Dreamweaver will use the virtual() function for including files. You should set this to Document instead so that Dreamweaver will use the require_once() function.

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  

"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"

The original site set up needed the BOM option set. Now that it runs on UTF-8 its not needed. Removing it cured the error message. Thanks for that one.

Now I just have to work out how to use iUE4 with a form.
Documentation for using it with forms does not seem to exist. Unlike UE3!