I'm facing problem in provisioning VM's on vCAC 6.0+ vCD 5.5 setup.
It fails with the error
A server error was encountered. Error requesting machine. Transactions with IsolationLevel Snapshot cannot be promoted.
I have checked and made sure that my DB and the model manager service is installed with the same username.
If you are using Iaas SQL DB authentication, you can check that changing to windows authentication. You can follow the instructions at https://communities.vmware.com/message/2342947. Always good have a backup/snapshot before you try anything.