With 9.0.9000.0, you could sometimes run into this issue if you reboot too early after installing. This will also be fixed in the next release.

Hi, this is a known issue with the testsign enable script. It only affects silent installation (e.g. by using msiexec /quiet); normal driver installation (by double-clicking the MSI file) will run normally. I'll fix this in the next release. In the meantime, you could use the following command to install the certificate manually:

certutil -addstore -f TrustedPublisher XCP-ng_Test_Signer.crt