Minimum firmware required:
Check your firmware version from 'settings - about phone - more information', under the 'Firmware revision number' and see below if the preconditions for this app are met:
Lumia 820 or Lumia 920: 1232.5957.1308.0000 and higher
Lumia 920T: 2041.0009.1308.1002 and higher
Lumia 520, Lumia 620 or Lumia 720: 1030.6407.1308.0000 and higher
Note: Lumia 810 and Lumia 822 do not currently have a firmware available that would have the necessary enablers in it
Did you even read the post above yours? In particular the words that Dustin Hodges was so kind to bold so that they would be more attenton-getting?1308 is available as my 820 has it... But yes you must be running this firmware for storage check to work...