Is this PowerShell version 5.1? We are aware of the incompatibility issue of current vRO PowerShell plug-in with version 5.1 of PowerShell, and we are working on a fix. Hopefully, an updated plug-in build will be released soon.
BTW, we have some customers reporting that this issue is not reproducible with the latest Windows versions (Windows 10/Windows Server 2016); only Windows 8/Windows Server 2012 and older versions are affected.
This error is caused when trying to add PS host running PowerShell 5.1. (on Windows Server 2012 R2)
We have just published technical preview version of the plugin that should resolve the issue hereTechnical preview version of VMware vCenter Powershell Plug-in 1.0.x