You are sure that it isn't declared within a function? Or do you try to use it in a function?
How about doing a really simple test. Make two files, test1.php and test2.php. In test2.php you do something with $sqlObj, very basic.
In test1.php you make the object like above and do:
code:
require("test2.php");
Still doesn't work? Then you should look to the server setting. Does it work now? Then it's your code. Maybe you did define or use it within a function. Use "global $sqlObj;" then.