activity workflow - powershell activity throwing Index was out of range

FIM WAL is calling a powershell activity. After the activity is called, search requests throws " this workflow instance encountered an internal error during processing". In event viewer, I could see this error. I even tried with empty try catch statement. Iit's giving the same error.

param($oid,$fname,$AcctName,$lname)
try
{
$line = "test"
}
catch [System.Exception]
{
 return "bad value"
}

System.ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection.
Parameter name: index
   at System.ThrowHelper.ThrowArgumentOutOfRangeException()
   at System.Collections.Generic.List`1.get_Item(Int32 index)
   at System.Collections.ObjectModel.Collection`1.get_Item(Int32 index)
   at FIM.Workflow.Common.Activities.RunPowerShellScript.RunScript(String script, ArrayList arguments, Dictionary`2 parameters)
   at FIM.Workflow.Common.Activities.RunPowerShellScript.Run_ExecuteCode(Object sender, EventArgs e)
   at System.Workflow.ComponentModel.Activity.RaiseEvent(DependencyProperty dependencyEvent, Object sender, EventArgs e)
   at System.Workflow.Activities.CodeActivity.Execute(ActivityExecutionContext executionContext)
   at System.Workflow.ComponentModel.ActivityExecutor`1.Execute(T activity, ActivityExecutionContext executionContext)
   at System.Workflow.ComponentModel.ActivityExecutor`1.Execute(Activity activity, ActivityExecutionContext executionContext)
   at System.Workflow.ComponentModel.ActivityExecutorOperation.Run(IWorkflowCoreRuntime workflowCoreRuntime)
   at System.Workflow.Runtime.Scheduler.Run()