Welcome to Android Central! Does this happen on both wi-fi and mobile data?
Here are a few things to try:
1. Go to Settings>Apps>All, select Google Play Store, Force Stop, then Clear Cache/Data. Do the same for Download Manager.
2. Go to Settings>Accounts, and remove your Google account from the device. Then add it back again.
3. Go to Google Wallet on the web and make sure your credit card info is valid.