Actually, you probably need to scrap that query entirely and explain what you are trying to do. You've got some inconsistent elements to your query.
1. You are using a DCOUNT in a AGGREGATE query. DCOUNT returns a count of fields in a table, but an AGGREGATE query allows that same functionality. It's probably redundant to use both.
2. All the fields in the GROUP BY clause are in the SELECT clause. And since every Expr1 is going to return the same value, you are just generating a list of unique National values. Usually you use an aggregate function on one or more of the fields in the SELECT clause and not include those fields in the GROUP BY clause.
You're query is really inconsistent, and even when you do get it to work, I bet it won't return the values you expect. So, provide us with some sample data from Employee (include field names) and then provide what you expect as the results from that sample data. Use this format:
Employee
Field1Name, Field2Name, Field3Name
David, 134, 5/15/2011
Larry, 435, 6/12/2008
Sally, 12, 1/1/2004