Syntax error in VTQL_Parser.php

If I open my calendar I got a warning that strtolower is not a constant.
Got error 'PHP message: PHP Warning: Use of undefined constant strtolower - assumed 'strtolower' (this will throw an Error in a future version of PHP) in include/Webservices/VTQL_Parser.php on line 1188PHP message: PHP Warning: Use of undefined constant strtolower - assumed 'strtolower' (this will throw an Error in a future version of PHP) in include/Webservices/VTQL_Parser.php on line 1335', referer: http://vtiger-test/index.php?module=Calendar&view=Calendar

line: 1188 if(!in_array("", $this->out["column_list"]) && !in_array("count()", array_map(strtolower, $this->out["column_list"]))){

line: 1335 }elseif( !in_array('count(*)', array_map(strtolower, $this->out['column_list']))){
I dont know what is here correct