iPad - Unable to Download Application / Update

Hi everyone, I'm having some trouble with my iPad 1.
Im currently running on the latest iOS and for many times I've tried to update some apps that are automatically show in my AppStore (btw - my iOS is not jailbroken).

When I click on the update button in AppStore I get a Message saying: "Unable to Download Application" on all of the apps.
What can this error be and how to fix it? Does anyone know?

I can download the updates thru the MAC via iTunes and then sync, but I want to be able to update them vía my iPad directly.

Appreciate your help!

Thanks,