Customized MSSQL Datasource failed!

[wilsonlms]

I am now using the latest Microsoft Windows zenpack 2.6.1. Under the "SQL instances" component, I created a datasource with the following information but failed to retrieve the counter. Any hints?

Strategy : Custom Command
Parser : Auto
Use Powershell : checked
Script : get-counter -computer '${here/id}' -counter "\SQLServer:Buffer Manager\Page life expectancy";

A warning event complains about the access problem :
"Custom Command error: Get-Counter : Unable to access the desired computer or service. Check the permissions and authentication of the log service or the interactive user session against those on the computer or service being monitored."