My iPhone won't automatically update apps anymore. Why?

I receive notifications of updates to my apps. I used to click on "update all", give password when prompted and "viola" all the app updates download. It worked perfectly. Now, it asks me to sign in to iTunes by entering my AppleID password. I enter my password. It doesn't say anything about password being incorrect but simply returns to the list of apps with updates and doesn't download them. Repeat...same result.