Process.StartTime Access Denied

using System.Management;
String queryString = "select CreationDate from Win32_Process where ProcessId='" + ProcessId + "'";
SelectQuery query = new SelectQuery(queryString);

ManagementScope scope = new System.Management.ManagementScope(@"\.rootCIMV2");
ManagementObjectSearcher searcher = new ManagementObjectSearcher(scope, query);
ManagementObjectCollection processes = searcher.Get();

    //... snip ... logic to figure out which of the processes in the collection is the right one goes here

DateTime startTime = ManagementDateTimeConverter.ToDateTime(processes[0]["CreationDate"].ToString());
TimeSpan uptime = DateTime.Now.Subtract(startTime);