・Caused by security software or some other software.
When you use the security software or some other resident softwares, once stop them all and activate again.
　Pay attention to not only anti-virus software like Norton or security software but also utility software of your mouse.

・Check the serial code whether it isn’t wrong.
Check your entered serial code* whether it hasn’t typographical error.
*16 digit number without hyphen
Pay attention not to mistake when you enter the product key because the letters 0 and O, 8 and B, 1 and I or l are resemble each other.

・Date and time aren’t correct on your PC.
When date and time of your system aren’t correct, you may fail the activation.
Check date and time whether they are set correctly.

・The settings of the proxy server.
You are required to set the proxy server depending on your internet provider.
In this case, if you set the proxy to the Internet Explorer, you may be able to execute the activation.

・The setting of the internet option
When you are using Windows, check whether there is a check mark on “use TLS 1.2” at the setting column in the advanced settings of the internet option.
If there isn’t a check mark, after you place it and confirm with [OK], reboot your computer.
Control panel → Internet option → Advanced settings

For details, please check the Yamaha website below.
https://www.vocaloid.com/en/news/about_change_authorization_tls/

・Update Vcaloid License Manager
When you are using mac, try to apply the updata which is published on the website of YAMAHA below.
*When you are using macOS10.9～macOS10.10, it supports only offline activation.
https://www.vocaloid.com/en/support/download/license-manager-mac/