Admin components error

hi, i am using wp 2.7.1 and ar the admin widgets page components are not displayed first and when i try to add one it gives me;
“Fatal error: Allowed memory size of bytes exhausted (tried to allocate bytes) in /wp-admin/includes/widgets.php on line 108” then;
“Fatal error: Allowed memory size of 67108864 bytes exhausted (tried to allocate 126372 bytes) in /home/xxxx/public_html/wp-admin/includes/widgets.php on line 95”. then i want to try another theme, it gives me that error;
“Fatal error: Allowed memory size of 67108864 bytes exhausted (tried to allocate 71 bytes) in /home/xxxxx/public_html/wp-includes/wp-db.php on line 808”. and still does’nt show my all component.
why occured errors? and how can i fix it? thanks