civiCRM有时候会报出下面错误，为什么吗？

civiCRM有时候会报出下面错误，为什么吗？

nitialization Error

Array
(
    [callback] => Array
        (
            [0] => CRM_Core_Error
            [1] => simpleHandler
        )

    [code] => -14
    [message] => DB Error: no database selected
    [mode] => 16
    [debug_info] => SELECT locale_custom_strings FROM civicrm_domain WHERE id = 1 [nativecode=2027 ** Malformed packet]
    [type] => DB_Error
    [user_info] => SELECT locale_custom_strings FROM civicrm_domain WHERE id = 1 [nativecode=2027 ** Malformed packet]
    [to_string] => [db_error: message="DB Error: no database selected" code=-14 mode=callback callback=CRM_Core_Error::simpleHandler prefix="" info="SELECT locale_custom_strings FROM civicrm_domain WHERE id = 1 [nativecode=2027 ** Malformed packet]"]
)