This means that OH cannot download and install the configured add-ons.
First restart OH.
If that doesn’t clear it up, try Clear the Cache.
If that doesn’t work, check your network and firewall settings. Something is preventing OH from reaching the service where the add-ons are downloaded from on the Internet.
As a last step, you can download the add-ons.kar file that corresponds to your version of OH (release, milestone, snapshot) from Download openHAB | openHAB. Place that file into the addons folder (see the installation instructions page for your OS for where that folder is) and OH will get the add-ons from the kar file instead of the Internet. But remember when you upgrade OH you’ll have to download the kar file again.