WP grins ‘Warning’

Hi,

I just installed WordPress Grins onto my blog(https://dispiacere.org) using these instructions: https://dev.wp-plugins.org/file/wp-grins/trunk/README.txt

Now, however, everytime I go to update a page or a post, I get this message:

Warning: Cannot modify header information – headers already sent by (output started at /home/bel/public_html/wp-content/plugins/wp-grins.php:2) in /home/bel/public_html/wp-admin/inline-uploading.php on line 138

I’m not really sure wherther the lines with no space count as lines or not..so I can’t find the line,
but does anyone know what is causing the error?
Thanks.