opencart 进不去后台

装好opencart 进入后台，页面出现如下错误：Fatal error: Uncaught exception 'Exception' with message 'Error: MySQL server has gone away<br />Error No: 2006<br />UPDATE ocr1_currency SET value = '1.00000', date_modified = '2016-11-08 00:01:14' WHERE code = 'USD'' in /home/goodtt75/public_html/system/library/db/mysqli.php:40 Stack trace: #0 /home/goodtt75/public_html/system/library/db.php(16): DB\MySQLi->query('UPDATE ocr1_cur...', Array) #1 /home/goodtt75/public_html/admin/model/localisation/currency.php(144): DB->query('UPDATE ocr1_cur...') #2 [internal function]: ModelLocalisationCurrency->refresh() #3 /home/goodtt75/public_html/system/engine/loader.php(178): call_user_func_array(Array, Array) #4 [internal function]: Loader->{closure}(Array, Array) #5 /home/goodtt75/public_html/system/engine/proxy.php(25): call_user_func_array(Object(Closure), Array) #6 /home/goodtt75/public_html/admin/controller/common/dashboard.php(87): Proxy->__call('refresh', Array) #7 /home/goodtt75/public_html/admin/controller/common/dashboard.php(87): Proxy->refresh() #8 [internal function] in /home/goodtt75/public_html/system/library/db/mysqli.php on line 40
请各位指点。