Hello everyone.
I had the same issue on a virtual applience. Boris solution worked for me as well.
1. Connect to the Transporter via SSH (for instance with Putty)
2. cd /opt/nakivo/transporter
3. ./bhsvc stop
./bhsvc -b "<UsePassword>" (creates a masterpassword)
./bhsvc start
4. Go to the Nakivo configuration > Transporter > edit > enter the masterpassword and connect > accept the certificate
5. Fixed and working again.
Cheers