OAI-PMH upgrade error

Omeka has encountered an error

Zend_Db_Statement_Mysqli_Exception
Mysqli statement execute error : Table 'omeka.omeka_oaipmh_harvester_harvests' doesn't exist

#0 /var/www/application/libraries/Zend/Db/Statement.php(303): Zend_Db_Statement_Mysqli->_execute(Array)
#1 /var/www/application/libraries/Zend/Db/Adapter/Abstract.php(480): Zend_Db_Statement->execute(Array)
#2 [internal function]: Zend_Db_Adapter_Abstract->query('ALTER TABLE `om...')
#3 /var/www/application/libraries/Omeka/Db.php(79): call_user_func_array(Array, Array)
#4 /var/www/plugins/OaipmhHarvester/OaipmhHarvesterPlugin.php(140): Omeka_Db->__call('query', Array)
#5 /var/www/plugins/OaipmhHarvester/OaipmhHarvesterPlugin.php(140): Omeka_Db->query('ALTER TABLE `om...')
#6 [internal function]: OaipmhHarvesterPlugin->hookUpgrade(Array)
#7 /var/www/application/libraries/Omeka/Plugin/Broker.php(145): call_user_func(Array, Array)
#8 /var/www/application/libraries/Omeka/Plugin/Installer.php(99): Omeka_Plugin_Broker->callHook('upgrade', Array, Object(Plugin))
#9 /var/www/application/controllers/PluginsController.php(185): Omeka_Plugin_Installer->upgrade(Object(Plugin))
#10 /var/www/application/libraries/Zend/Controller/Action.php(516): PluginsController->upgradeAction()
#11 /var/www/application/libraries/Zend/Controller/Dispatcher/Standard.php(308): Zend_Controller_Action->dispatch('upgradeAction')
#12 /var/www/application/libraries/Zend/Controller/Front.php(954): Zend_Controller_Dispatcher_Standard->dispatch(Object(Zend_Controller_Request_Http), Object(Zend_Controller_Response_Http))
#13 /var/www/application/libraries/Zend/Application/Bootstrap/Bootstrap.php(97): Zend_Controller_Front->dispatch()
#14 /var/www/application/libraries/Zend/Application.php(366): Zend_Application_Bootstrap_Bootstrap->run()
#15 /var/www/application/libraries/Omeka/Application.php(79): Zend_Application->run()
#16 /var/www/admin/index.php(28): Omeka_Application->run()
#17 {main}

It looks like you somehow have the plugin in a state where Omeka thinks it's been previously installed, but the tables aren't actually there.

The easiest thing to do is probably just to manually delete the OaipmhHarvester record from your omeka_plugins table. That will make Omeka "forget" about the old Harvester installation it thinks its upgrading and let you choose Install instead.