error message after installed plugin

hi. Hope you can help! I installed a plugin from seologs.com (the “blogthis” plugin). But ever since my blog is a mess, particularlyt the header. I’m not getting this message:

Warning: include_once(/home/janbanis/public_html/easyonlinebusinessinfo/wp-content/plugins/__MACOSX/) [function.include-once]: failed to open stream: Success in /home/janbanis/public_html/easyonlinebusinessinfo/wp-settings.php on line 473

Warning: include_once() [function.include]: Failed opening ‘/home/janbanis/public_html/easyonlinebusinessinfo/wp-content/plugins/__MACOSX/’ for inclusion (include_path=’.:/usr/lib/php:/usr/local/lib/php’) in /home/janbanis/public_html/easyonlinebusinessinfo/wp-settings.php on line 473

Warning: Cannot modify header information – headers already sent by (output started at /home/janbanis/public_html/easyonlinebusinessinfo/wp-settings.php:473) in /home/janbanis/public_html/easyonlinebusinessinfo/wp-login.php on line 255

Warning: Cannot modify header information – headers already sent by (output started at /home/janbanis/public_html/easyonlinebusinessinfo/wp-settings.php:473) in /home/janbanis/public_html/easyonlinebusinessinfo/wp-login.php on line 267

The plugin was installed using the installation feature in wordpress 2.7, so it was installed directly from the zipfile on my desktop. However, when I checked the plugin folder in my ftp client, i noticed that some folder called _MACOSX was also installed/copied. Anyway I deleted the lots, which may be the reason why the last 2 error messages dont have a reference to that folder in it.

I know nothing about php and just want to rectify this as soon as possible. Thanks so much for any help.

Jan