Make sure that you do not have a stalled download in iTunes - a song or podcast .... if you have a download in there that did not finish, complete that one first. Only one thing can download at a time on the iPad so that could be what is causing the problem.
If that doesn't work - sign out of your account, restart the iPad and then sign in again.
Settings>Store>Apple ID. Tap your ID and sign out. Restart the iPad by holding down on the sleep button until the red slider appears and then slide to shut off. To power up hold the sleep button until the Apple logo appears and let go of the button.
Go back to Settings>Store>Sign in and then try to update again. Tap one waiting icon only if necessary to start the download stream.
You can also try deleting the waiting icons - tap and hold down on an icon until it wiggles - the tap the X on the icon to delete it. Then try to download again.
You can try resetting all settings. Settings>General>Reset>Reset All Settings. You will have to enter all of your app preferences and device settings again.