Starting Azure Vm in parallel with runbook throws InvalidOperationException

Question

I'm trying to use Azure runbooks to start virtual machines with a specified tag. I use powershell workflow so i can start them i parallel.

The code below works, but it always have problem starting one random virtual machine. This is the exception:

Start-AzureRmVM : Collection was modified; enumeration operation may not execute.

CategoryInfo : CloseError: (:) [Start-AzureRmVM], InvalidOperationException

I thought $TaggedResourcesList = @($Resources) would enumerate the list and make modifications allowed?

workflow StartUpParallel 
{

    $Resources = Find-AzureRmResource -TagName Startup -TagValue PreWork
    $TaggedResourcesList = @($Resources)

    Foreach -Parallel ( $vm in $TaggedResourcesList ) 
    {
        if($vm.ResourceType -eq "Microsoft.Compute/virtualMachines") 
        {
            Start-AzureRmVM -ResourceGroupName $vm.ResourceGroupName -Name $vm.Name    
        }
    }
}

Has anyone else had this problem?