I had the exact same problem. I could go to iTunes (on my iPad 2) but couldn't update the apps. I tried two things. The first worked for my son's iPad 2, which was to sign out, close the store, sign back in with a different persons iTunes infomation, sign out, close again, reopen the store and enter the owners information. This worked for him, but not for mine.
Second thing I did, that worked for mine was to close everything on the iPad, go into the date/time setting. Change the date to about 4 years in the future (2016), then close. I went to iTunes to update my apps and got an error message about the date being wrong. I force closed everything, opened up the date and reset it to the current date. Went back to update my apps and everything was fine. Try it and let me know if it works for you!!!