[Plugin: Wp_cron] Task not executing

Hi everyone.

I have an issue with a plugin i am developing.
This plugin has to run every 3 hours and connect to some remote server to grab some json data. I set up the cron tasks which appears properly and the plug in display the time remaining to the next update.
Problem is that when the time for the update comes no data is grabbed at all. When i runs it manually data is grabbed properly and there is no error.

Also i have been installing ‘Cron Control’ plugin in order to run the cron directly from the admin. When i do it no problem either, i just get ‘the selected task has been run properly’.
Does anyone know Why the cron would run properly when i manually do it and not when it is completely automated ?

Thank you in advanced,