Missing File -1000's in error log

The SEFA error log reports this URL -  administrator/plugins/system/pc_includes/ajax_1.2.js  -  as missing, it appears to have been going on for a while as there are over 8000 hits/misses for it.

The referrer is shown to be:  ****/administrator/index.php?option=com_sef&c=logs

Any idea on how to fix this?  THanks