Hello,
How many licenses have you installed? How many servers are you backing up?(Exchange,SQL...etc) Where exactly do you get this error?
You can try:
Resolution 1:
To resolve this, uninstall and re-install the license key.
1) Go to Tools > Install Options and License keys on this Media Server
2) Select the key that is installed, but not showing inside the license information window.
3) Select the remove button.
4) Select Next > Next > Install
5) Go to Tools > Install Options and License keys on this Media Server
6) Add the license key then select Add
7) Select Next > Next > Install
8) Restart the services and attempt the backup again.
Resolution 2:
If Resolution 1 did not resolve the issue, then there is possibly another service such as an Anti-Virus that may be blocking the license from a proper installation.
1) Temporarily disable the suspected service.
2) Go to Tools > Install Options and License keys on this Media Server
3) Select the key that is installed, but not showing inside the license information window.
4) Select the remove button.
5) Select Next > Next > Install
6) Go to Tools > Install Options and License keys on this Media Server
7) Add the license key then select Add
8) Select Next > Next > Install
9) Restart the services and attempt the backup again.
Hope this helps...