Constructor Error

Hi all

I've tried to change a Dialog Workflow with a plugin to a entity that on save runs the plugin to do the same thing. Problem is it produces the following error

Unexpected exception from plug-in (Constructor): Stan.ManholePrice: System.MissingMethodException: Constructor on type 'Stan.ManholePrice' not found.

I'm not sure if the plugin should now be a Iplugin insted of a codeactivity or am i just missing something in the code to enable it to run from an entity. Here is the start of the code and where i think the issue is. I have tried following some guides but they all seem to be based round the fact the plugin is an Iplugin

  public class ManholePrice : CodeActivity

    {

        #region Secure/Unsecure Configuration Setup

        private string _secureConfig = null;

        private string _unsecureConfig = null;

        public ManholePrice(string unsecureConfig, string secureConfig)

        {

            _secureConfig = secureConfig;

            _unsecureConfig = unsecureConfig;

        }

        #endregion

        protected override void Execute(CodeActivityContext executionContext)

        {

            //Create the tracing service

            ITracingService tracingService = executionContext.GetExtension<ITracingService>();

            //Create the context

            IWorkflowContext context = executionContext.GetExtension<IWorkflowContext>();

            IOrganizationServiceFactory serviceFactory = executionContext.GetExtension<IOrganizationServiceFactory>();

            IOrganizationService service = serviceFactory.CreateOrganizationService(context.UserId);

            // Create a column set to define which attributes should be retrieved.

            ColumnSet attributes = new ColumnSet(true);

            Entity currentPriceLevelEntity = new Entity("pricelevel");

            currentPriceLevelEntity = service.Retrieve("pricelevel", CurrentPriceList.Get<EntityReference>(executionContext).Id, attributes);

            // Create New Price List

            Entity newPriceLevel = new Entity("pricelevel");

            newPriceLevel["name"] = NewPriceListName.Get<string>(executionContext);

            newPriceLevel["transactioncurrencyid"] = currentPriceLevelEntity["transactioncurrencyid"];

            Guid newPriceLevelId = service.Create(newPriceLevel);

            newPriceLevel["Price900"] = ManholePrice900.Get<string>(executionContext);

            newPriceLevel["Price1050"] = ManholePrice1050.Get<string>(executionContext);

            newPriceLevel["Price1200"] = ManholePrice1200.Get<string>(executionContext);

Any advice would be greatly appreciated

Regards

Dan