Cannot burn on a virtual machine

I've installed EMS v.7.7.0 on a Windows 7 Virtual Machine. I've migrated an existing EMS database to this virtual machine. When I create a new entitlement and try to Produce a new key, I have this behavior:

* with some keys nothing happen: when I click the Burn button, I see the Loading... label but the key status remains to "Ready to Burn". When I return to Entitlements, the Status remains to Queued

* with other keys, when I click the Burn button, this error message appears "Activation failed with status code :999. could not extract ResultSet"

Can you help me?

Thanks,

Matteo