Incase anyone has this issue in the future, I managed to resolve this by fixing the permissions at the root of the access zone, they were far too restrictive and didn't allow execute / transfers permissions 
We have a production Isilon which has been fine for ages, and have setup a Simulator for a safer testing environment. The logic is exactly the same between the two and have just setup the delegated DNS to point to the simulator, however no matter what I do, I am always hit with an Access Denied pop up window when attempting to access the share via the correct access zone.  it almost appears the cluster is not doing lookups in AD correctly, SPN are set, DNS deletion is set, pinging results in correct round robin responses for the pool, Authenticator providers are set for the access zone as i can lookup groups for the SMB share permissions etc.. NFS mounts work fine, as we use NFSv3 so no authentication requirement. we are wanting to test specific NFS+SMB sharing of the same directories, however we always get 'Access is deinied' pop ups Are there any known bugs in the Simulator? or have i missed something this is 9.4.0.0 (on the simulator), we run 9.4.0.4 in our production cluster.     
Simulator Access Denied on smb