The web server is wrinting to this file. Web servers run under special very limited permissions for security reasons. You need to change the permissions on
library/sqlconf.php
to allow this to take place. As the root user
chmod 777 YourRealPath/library/sqlconf.php
Then change the permissions back to more secure permissions after completing the setup
chmod 644 YourRealPath/library/sqlconf.php
We can help more if you give us your operating system and the path to sqlconf.php.