Additional uncaught exception thrown while handling exception.

<h1>Additional uncaught exception thrown while handling exception.</h1><h2>Original</h2><p>PDOException: SQLSTATE[HY000]: General error: 2006 MySQL server has gone away: SELECT body, format FROM {block_custom} WHERE bid = :bid; Array
(
    [:bid] => 1
)
 in block_block_view() (line 245 of /mnt/panlin/modules/block/block.module).</p><h2>Additional</h2><p>PDOException: SQLSTATE[HY000]: General error: 2006 MySQL server has gone away: SELECT 1 AS expression
FROM 
{variable} variable
WHERE ( (name = :db_condition_placeholder_0) ); Array
(
    [:db_condition_placeholder_0] => drupal_css_cache_files
)
 in variable_set() (line 1260 of /mnt/panlin/includes/bootstrap.inc).</p><hr /><br />
<b>Fatal error</b>:  Uncaught exception 'PDOException' with message 'SQLSTATE[HY000]: General error: 2006 MySQL server has gone away' in /mnt/panlin/includes/database/database.inc:2278
Stack trace:
#0 /mnt/panlin/includes/database/database.inc(2278): PDOStatement->execute(Array)
#1 /mnt/panlin/includes/database/database.inc(744): DatabaseStatementBase->execute(Array, Array)
#2 /mnt/panlin/includes/database/database.inc(2457): DatabaseConnection->query('SELECT expire, ...', Array, Array)
#3 /mnt/panlin/includes/lock.inc(167): db_query('SELECT expire, ...', Array)
#4 /mnt/panlin/includes/lock.inc(146): lock_may_be_available('theme_registry:...')
#5 /mnt/panlin/includes/theme.inc(449): lock_acquire('theme_registry:...')
#6 /mnt/panlin/includes/bootstrap.inc(460): ThemeRegistry->set(Array)
#7 [internal function]: DrupalCacheArray->__destruct()
#8 {main}
  thrown in <b>/mnt/panlin/includes/database/database.inc</b> on line <b>2278</b><br />