Quoting Grandmother Spider gs@grandmother-spider.com:
...a bug in taxonomy.module that has not fully been fixed in the 4.7.6 release. I used the suggested changes, the "invalid" arguments stopped, and eventually the cron job now after about four minutes throws an "out of memory" error as it tries to work through search.module's cron. My php.ini is set to 64M.
You can increase the memory_limit in the .htaccess file. Add the following line at the bottom of the file to see if it helps.
php_value memory_limit 128M
Earnie