There was a call to $this->input->_remove_invisible_characters($str); It should have been:  $this->input->CI->_remove_invisible_characters($str);
diff --git a/system/database/drivers/mssql/mssql_driver.php b/system/database/drivers/mssql/mssql_driver.php
index fd3f963..9d7e072 100644
--- a/system/database/drivers/mssql/mssql_driver.php
+++ b/system/database/drivers/mssql/mssql_driver.php
@@ -214,7 +214,7 @@
 	function escape_str($str)	

 	{	

 		// Escape single quotes

-		return str_replace("'", "''", $this->input->_remove_invisible_characters($str));

+		return str_replace("'", "''", $this->CI->input->_remove_invisible_characters($str));

 	}

 	

 	// --------------------------------------------------------------------