zcat error_log*.gz | grep -P -o '(?<=Error code: )\w+' | sort | uniq -c | sort -nr

   3761 invalidsesskey

   1126 cannotregisternotavailablesite

    944 invalidid

    626 missingparam

    346 freshmoodleregistrationerror

    305 invalidqueryparam

    126 invalidcoursemodule

    105 invalidfile

     80 freshmoodleregistrationerror2

     46 invalidrecord

     30 accessdenied

     21 usernamenotfound

      9 errorwrongdata

      8 filenotfound

      8 dmlwriteexception

      7 blogdisable

      5 sslonlyaccess

      4 rpcerror

      4 dmlreadexception

      3 invalidarguments

      2 Sorry

      1 sectionerror

      1 requireloginerror

      1 notlocalisederrormessage

      1 invalidargorcon