Problem executing PowerCLI commands in workflow

I am trying to excute PowerCLI commands in a workflow and they are returning null for getHostOutput and getResults.  I have tried creating a PowerShellSession object and populating the info with addCommandFromString and addParameter and using invokePipeline.  I have also tried psHost.invokeScript as well as the Invoke a PowerShell script workflow.  If I use simple powershell commands (ex. Get-Date) any of the above work fine.  PowerCLI commands (ex. Get-Tag, Get-VM) return null.  However, they do throw correct errors when invalid information is provided.  Any ideas?

vCO 5.1.1