The VMware Studio connection wizard fails on vCenter 5, and on direct to ESX 5. If you skip using the connection wizard (and you get the parameters right), then the connection to either vCenter 5 or ESXi 5 does work. (At least it works here.)
However, we did switch from connecting through the vCenter to connecting direct to the ESX host. The connection through the vCenter was just too prone to random failures. We still get failures, just not as many, when connecting direct to the ESX host.