Mysqli statement execute error

Omeka 1.5.1 I am getting this error when I try and add tags to an item, or when I try and edit a description. Stack trace below.
(I have other Omeka projects on the same server, versions 1.4 and 1.5, and I do not get this error.)

2012-10-23T16:22:13+04:00 ERR (3): exception 'Zend_Db_Statement_Mysqli_Exception' with message 'Mysqli statement execute error : Column 'text' cannot be null' in /home/ctevans/public_html/Memory/application/libraries/Zend/Db/Statement/Mysqli.php:214

Stack trace:
#0 /home/ctevans/public_html/Memory/application/libraries/Zend/Db/Statement.php(300): Zend_Db_Statement_Mysqli->_execute(Array)
#1 /home/ctevans/public_html/Memory/application/libraries/Zend/Db/Adapter/Abstract.php(479): Zend_Db_Statement->execute(Array)
#2 [internal function]: Zend_Db_Adapter_Abstract->query('? INSERT...', Array)
#3 /home/ctevans/public_html/Memory/application/libraries/Omeka/Db.php(83): call_user_func_array(Array, Array)
#4 /home/ctevans/public_html/Memory/application/libraries/Omeka/Db.php(297): Omeka_Db->__call('query', Array)
#5 /home/ctevans/public_html/Memory/application/libraries/Omeka/Db.php(297): Omeka_Db->query('? INSERT...', Array)
#6 /home/ctevans/public_html/Memory/application/libraries/Omeka/Db.php(267): Omeka_Db->exec('? INSERT...', Array)
#7 /home/ctevans/public_html/Memory/application/libraries/Omeka/Record.php(551): Omeka_Db->insert('ElementText', Array)
#8 /home/ctevans/public_html/Memory/plugins/PdfSearch/PdfSearchPlugin.php(148): Omeka_Record->save()
#9 /home/ctevans/public_html/Memory/plugins/PdfSearch/PdfSearchPlugin.php(123): PdfSearchPlugin->saveFilePdfText(Object(File), 86, 2)
#10 /home/ctevans/public_html/Memory/plugins/PdfSearch/PdfSearchPlugin.php(97): PdfSearchPlugin->saveItemPdfText(Object(Item), 86, 2)
#11 [internal function]: PdfSearchPlugin->hookAfterSaveItem(Object(Item))
#12 /home/ctevans/public_html/Memory/application/libraries/Omeka/Plugin/Broker.php(156): call_user_func_array(Array, Array)
#13 /home/ctevans/public_html/Memory/application/libraries/Omeka/Plugin/Broker.php(182): Omeka_Plugin_Broker->callHook('after_save_item', Array)
#14 [internal function]: Omeka_Plugin_Broker->__call('after_save_item', Array)
#15 [internal function]: Omeka_Plugin_Broker->after_save_item(Object(Item))
#16 /home/ctevans/public_html/Memory/application/libraries/Omeka/Record.php(304): call_user_func_array(Array, Array)
#17 /home/ctevans/public_html/Memory/application/libraries/Omeka/Record.php(566): Omeka_Record->runCallbacks('afterSave')
#18 /home/ctevans/public_html/Memory/application/libraries/Omeka/Record.php(807): Omeka_Record->save()
#19 /home/ctevans/public_html/Memory/application/libraries/Omeka/Controller/Action.php(482): Omeka_Record->saveForm(Array)
#20 /home/ctevans/public_html/Memory/application/controllers/ItemsController.php(99): Omeka_Controller_Action->editAction()
#21 /home/ctevans/public_html/Memory/application/libraries/Zend/Controller/Action.php(516): ItemsController->editAction()
#22 /home/ctevans/public_html/Memory/application/libraries/Zend/Controller/Dispatcher/Standard.php(295): Zend_Controller_Action->dispatch('editAction')
#23 /home/ctevans/public_html/Memory/application/libraries/Zend/Controller/Front.php(954): Zend_Controller_Dispatcher_Standard->dispatch(Object(Zend_Controller_Request_Http), Object(Zend_Controller_Response_Http))
#24 /home/ctevans/public_html/Memory/application/libraries/Zend/Application/Bootstrap/Bootstrap.php(97): Zend_Controller_Front->dispatch()
#25 /home/ctevans/public_html/Memory/application/libraries/Zend/Application.php(366): Zend_Application_Bootstrap_Bootstrap->run()
#26 /home/ctevans/public_html/Memory/application/libraries/Omeka/Core.php(165): Zend_Application->run()
#27 /home/ctevans/public_html/Memory/admin/index.php(44): Omeka_Core->run()
#28 {main}

This looks to be coming from the PdfSearch plugin.

Deactivating that plugin would probably solve this problem, but I'm not sure exactly why it's happening.

Thanks. Deactivated the plugin, and the error disappeared. Upgraded to the newer version of the plugin, and the problem reappeared. So, it is now deactivated again.