Are you able to see the error in the viewcomposer logs on the composer server? This would be the first place to look as to why it is failing.
In the past if a host was in MM provisioning can fail because the host is simply in MM.
Hi, it sounds like the data store being used cannot be written to. If you browse to the data store in question using vCenter, are you able to create an empty folder in it? I found the below article which looks to be similar to the error you are seeing with your data store. It sounds like a permissions issue.