Error Description: 0x800B0109: A certificate chain processed, but terminated in a root certificate which is not trusted by the trust provider.

Possible Cause: This issue may occur if the appropriate trusted root certification authority (CA) certificate is not installed in the Trusted Root Certification Authorities store on the client computer.

Note: Generally the VPN client machine is joined to the active directory based domain and if you use domain credentials to log on to the VPN server, the certificate is automatically installed in the Trusted Root Certification Authorities store. However, if the computer is not joined to the domain or if you use an alternative certificate chain, you may experience this issue.

Possible Solution: Make sure root certificate is installed on the client machine in the Trusted Root Certification Authorities store.