Could not create VM Checkpoint Error (2923)

Hello,
I have a problem doing a checkpoint of a VM.
The job will fail with error message:

Error (2923)
A malformed response was received while trying to contact the VMM agent on HOSTNAME.DOMAIN.com.
Unspecified error (0x80004005)

Recommended Action
1) Ensure the VMM agent is installed and that the SCVMMAgent service is running.
2) If the SCVMMAgent service is running, restart the service, and then verify that WS-Management is installed correctly and that the WinRM service is running.
3) Check the manufacturers' Web sites to ensure that you have the latest drivers for your network adapters and other devices.

Do you have any idea whats wrong?
VMM agent ist installed and SCVMMAgent is running fine.

Best regards

Tobus