Plugin passing data problem how to solve?

Hello Experts

I registered my plugin with pre and post operations to share data between plugins .In shared variables I am able to store the variable .but I can't retrieve in other plugin .shared variables is accessed  in post operation. 

plugin 1 :

 Entity accountentity = new Entity();
                    // Refer to the account in the task activity.

                    // Obtain the organization service reference.
                    IOrganizationServiceFactory serviceFactory = (IOrganizationServiceFactory)serviceProvider.GetService(typeof(IOrganizationServiceFactory));
                    IOrganizationService service = serviceFactory.CreateOrganizationService(context.UserId);
                    Guid contactid = context.PrimaryEntityId;
                    context.SharedVariables.Add("AccountGUID",(Object)contactid.ToString());

plugin2:

      if (context.InputParameters.Contains("Target") &&
                context.InputParameters["Target"] is Entity)
            {
                // Obtain the target entity from the input parmameters.
                Entity entity = (Entity)context.InputParameters["Target"];

                // Verify that the target entity represents an account.
                // If not, this plug-in was not registered correctly.
                if (entity.LogicalName != "account")
                    return;

                try
                {
                    // Create a task activity to follow up with the account customer in 7 days. 
                    Entity accountentity = new Entity();                                      
                    // Refer to the account in the task activity.

                    // Obtain the organization service reference.
                    IOrganizationServiceFactory serviceFactory = (IOrganizationServiceFactory)serviceProvider.GetService(typeof(IOrganizationServiceFactory));
                    IOrganizationService service = serviceFactory.CreateOrganizationService(context.UserId);

                    if (context.SharedVariables.Contains("AccountGUID"))
                    {
                        Guid customerid = (Guid)context.ParentContext.SharedVariables["AccountGUID"];
                        Entity entitytask = new Entity("task");
                        entitytask["regardingobjectid"] = new EntityReference
                        {
                            LogicalName = "account",
                            Id = customerid
                        };
                        entitytask["subject"] = "Send an Email to new Custoemr";
                        service.Create(entitytask);

                    }
                    //var contactid = context.PrimaryEntityId;

}

in plugin 2 the sharedvariables does n't contain that variable ?why if any one suggest helpful

thanks and regards

Murali