pdo_driver.php, _escape_str($str) keeps returning FALSE

Hi.

I'm currently encountering a weird problem with version 3.0.6 of CodeIgniter.

I have two setups, one for development and one for production. Both are not using the same driver (because of configuration problem on my development computer) but are connected to the same DB

Prod use [sqlsrv], while Dev use [PDO] with dsn params: ['dsn' => 'odbc:Driver={SQL Server};...]

While using the query builder, the string is escaped using [protected function _escape_str($str)] in pdo_driver.php
in this function, [$strQuote = $this->conn_id->quote($str)] always return FALSE.

Just to set the variables, I'm experiencing this problem only in my development environment which is using PDO

I'm using phpEd as code editor and debug tool, but I cannot enter [conn_id->quote($str)] in debug mode to understand what is the problem.  it keeps sending me FALSE without any errors nor exception output.

Can anyone tell me where this function is declared, or help me resolve this situation?
else, I will need to modify this core function, witch is not a very good idea...  

Thanks