Problems with submissions

Hi
Im new to drupal and have encountered a problem.
When i want change permissions in admin/people/permissions, i makes an error page:

Additional uncaught exception thrown while handling exception.
Original
PDOException: SQLSTATE[HY000]: General error: 2006 MySQL server has gone away: SELECT * FROM {menu_links} WHERE menu_name = :menu_name AND module = :module AND link_path = :path; Array ( [:menu_name] => management [:module] => system [:path] => admin ) in toolbar_get_menu_tree() (line 286 of /var/www/web/gb1487/drupal/modules/toolbar/toolbar.module).

Additional
PDOException: SQLSTATE[HY000]: General error: 2006 MySQL server has gone away: INSERT INTO {watchdog} (uid, type, message, variables, severity, link, location, referer, hostname, timestamp) VALUES (:db_insert_placeholder_0, :db_insert_placeholder_1, :db_insert_placeholder_2, :db_insert_placeholder_3, :db_insert_placeholder_4, :db_insert_placeholder_5, :db_insert_placeholder_6, :db_insert_placeholder_7, :db_insert_placeholder_8, :db_insert_placeholder_9); Array ( [:db_insert_placeholder_0] => 1 [:db_insert_placeholder_1] => php [:db_insert_placeholder_2] => %type: !message in %function (line %line of %file). [:db_insert_placeholder_3] => a:6:{s:5:"%type";s:12:"PDOException";s:8:"!message";s:260:"SQLSTATE[HY000]: General error: 2006 MySQL server has gone away: SELECT * FROM {menu_links} WHERE menu_name = :menu_name AND module = :module AND link_path = :path; Array ( [:menu_name] => management [:module] => system [:path] => admin ) ";s:9:"%function";s:23:"toolbar_get_menu_tree()";s:5:"%file";s:57:"/var/www/web/gb1487/drupal/modules/toolbar/toolbar.module";s:5:"%line";i:286;s:14:"severity_level";i:3;} [:db_insert_placeholder_4] => 3 [:db_insert_placeholder_5] => [:db_insert_placeholder_6] => http://baboum.dk/drupal/admin/people/permissions [:db_insert_placeholder_7] => http://baboum.dk/drupal/node [:db_insert_placeholder_8] => 2.108.48.74 [:db_insert_placeholder_9] => 1352977650 ) in dblog_watchdog() (line 154 of /var/www/web/gb1487/drupal/modules/dblog/dblog.module).

--------------------------------------------------------------------------------

Uncaught exception thrown in session handler.
PDOException: SQLSTATE[HY000]: General error: 2006 MySQL server has gone away in _drupal_session_write() (line 209 of /var/www/web/gb1487/drupal/includes/session.inc).

--------------------------------------------------------------------------------

Fatal error: Exception thrown without a stack frame in Unknown on line 0

Can any one help ? what have i don wrong :-)
Best regards
Søren Lund
Denmark