[wp-hackers] headers error when making a plugin

[Bobby]

Ying Zhang wrote:

>hi, i'm writing my first wp plugin, it deals with the_content.. i have
>no idea why but now after i activated it, i'm getting
>
>Warning: Cannot modify header information - headers already sent by
>(output started at
>/home/pure/public_html/wp-content/plugins/multiple_more.php:80) in
>/home/pure/public_html/wp-admin/post.php on line 146
>
>my plugin is attached. it's not completed. i'm just grabbing some old
>code from my b2 hack. thanks for the help
>  
>
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These sorts of errors are 90% of the time caused by spaces or line 
breaks after the ending ?> of the plugin file. There can be no 
whitespace at the end of the file.