Get Current Form Record using on-Demand Workflow

Hi,

I have created one on-demand workflow.  

when I am trying to execute the workflow, I am getting error as

"Unexpected exception from plug-in (Execute): SCRM.Calculation: System.AggregateException: One or more errors occurred. If you contact support, please provide the technical details."

I want to access current form record using on-demand workflow.  

I am casting entity like

"   Entity entity = (Entity)context.InputParameters["Target"];
                new_student _studentinfo = entity.ToEntity<new_student>();"

in c# code.

Can anyone suggest, how to get current form record using on-demand workflow.