If you are experiencing, a similar error to below:
Fatal error: Uncaught Error: Function name must be a string in C:\xampp\htdocs\acf\lib\Varien\File\Uploader.php on line 259
This happens because in you are running Magneto 1.9 in PHP 7. To solve the error you need to clarify that you are going to call the $callback variable as a method (function).
Navigate to the original line of the code in file:
Find the line ~line 259
And replace it with