Fatal error upgrading drupal

Hello,

hope there is the good place to ask for help?

I just make an update on my drupal website same as always but before the end of it i get FATAL error ;o(

I cannot access to my admin !?!

A copy of the white page and error message :
Fatal error: Uncaught exception 'PDOException' with message 'SQLSTATE[HY000]: General error: 2006 MySQL server has gone away' in /home/chefscon/www/includes/database/database.inc:2171 Stack trace: #0 /home/chefscon/www/includes/database/database.inc(2171): PDOStatement->execute(Array) #1 /home/chefscon/www/includes/database/database.inc(683): DatabaseStatementBase->execute(Array, Array) #2 /home/chefscon/www/includes/database/database.inc(2350): DatabaseConnection->query('SELECT expire, ...', Array, Array) #3 /home/chefscon/www/includes/lock.inc(167): db_query('SELECT expire, ...', Array) #4 /home/chefscon/www/includes/lock.inc(146): lock_may_be_available('theme_registry:...') #5 /home/chefscon/www/includes/theme.inc(449): lock_acquire('theme_registry:...') #6 /home/chefscon/www/includes/bootstrap.inc(455): ThemeRegistry->set(Array) #7 [internal function]: DrupalCacheArray->__destruct() #8 {main} thrown in /home/chefscon/www/includes/database/database.inc on line 2171

Thanks for your help,