three solutions are proposed at the joomla forum
http://forum.joomla.org/viewtopic.php?f=428&p=1285404
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1)
I have finally found how to correct this problem.
In the backend—-> Configuration —–>System
On the right side there are settings for the cache.
In Port: I have put the value 0
….and it worked. No error message anymore.
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2) change the code on line 83 from :
[PHP]$this->_db->addServer($server[‘host’], $server[‘port’], $this->_persistent);[/PHP]
to
[PHP]$this->_db->addServer($server[‘host’], (int)$server[‘port’], $this->_persistent);
^^^^ see the cast to int?[/PHP]
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3) change the cache handler in Config -> System to be “File”. I believe this should be the default setting, and for whatever reason it changed to memcache.