The double backslash isn’t the issue. The problem is a mismatch between your PHP build and the drivers.
* Check if PHP is **x86 or x64** and **NTS or TS** (`phpinfo()` shows this).
* Use only the matching DLLs (e.g., for 32-bit NTS: `php_sqlsrv_74_nts_x86.dll` + `php_pdo_sqlsrv_74_nts_x86.dll`).
* Remove incorrect DLL entries from `php.ini`.
* Install the **Microsoft ODBC Driver for SQL Server** and the required **VC++ Redistributable**.
Then restart Apache and check `phpinfo()` for `sqlsrv`.
Some PHP extensions may not be enabled in 5.5/5.6 (check mysqli, mbstring, etc.). Older Joomla or plugins may use deprecated mysql_* functions. Turn on error reporting in php.ini to see what’s failing.
Confirm you edited the correct php.ini for each PHP version (phpinfo() helps).