Single Sign On (SSO) issue with vCenter 5.1

vCenter Server 5.1.0 build 880146

Problem hosts are  ESXi 4.1.0 build 433742

Hi-

We are having an issue in which our enterprise monitoring server (OpManager VM) cannot log into certain hosts in our environment, throwing an error in the log every couple of seconds. All problem hosts are still on ESXi 4.1 while hosts on 5.1 are not having this problem.

So my question is this- Does SSO even work with hosts running ESXi 4.1.0?