Warning messages

How do I fix this?

Warning: main(/homepages/43/d249753155/htdocs/blog/wp-content/plugins/twitter-tools/) [function.main]: failed to open stream: Success in /homepages/43/d249753155/htdocs/blog/wp-settings.php on line 465

Warning: main() [function.include]: Failed opening ‘/homepages/43/d249753155/htdocs/blog/wp-content/plugins/twitter-tools/’ for inclusion (include_path=’.:/usr/lib/php’) in /homepages/43/d249753155/htdocs/blog/wp-settings.php on line 465

Warning: Cannot modify header information – headers already sent by (output started at /homepages/43/d249753155/htdocs/blog/wp-settings.php:465) in /homepages/43/d249753155/htdocs/blog/wp-includes/pluggable.php on line 850

When I try to deactivate my plug-ins, the screen turns white and continues to show this message. I have been unable to update to 2.7 also.