The first variable of #{dataCentre} is read from a variable set assigned to the project, but is not being substituted. The second of #{Octopus.Environment.Name} is read from the environment it is being deployed to (Dev, QA, UAT, Staging, Production) and is being substituted.
Thanks for getting in touch! I may need to get some additional information from you to troubleshoot this issue. Would you be able to attach a full deployment log with variable logging enabled? This will give me a good idea of what could be going on during your deployment.