Unknown commit parameter 'waitFlush'

When I am in the settings of the plugin and I click “Load all Pages” or “Load all Posts” and it is not successful. If I go to the SOLR admin screen in the browser I see the error:
org.apache.solr.common.SolrException: Unknown commit parameter 'waitFlush'.

I am using SOLR 4.3. I also tried to replace the SolrPhpClient with the most recent one (https://code.google.com/p/solr-php-client/downloads/detail?name=SolrPhpClient.r60.2011-05-04.zip). Any ideas anyone?

http://ww.wp.xz.cn/extend/plugins/solr-for-wordpress/