first don't leave the value empty. becoz pkg will fail to validate if u leave empty. put anyvalue, becoz this value is changed during the execution.

Second why string? if its a count why not int or even bigint?....

U don't have to do anything on paramater tab..........leave it empty...........just map it to the resultset tab only the way i have said

put value to something.............this will work..........

and also if ur using as string, then you might to do as Acst in your script.....but thats on you.