FilterOperator.TopN problem

[Forest]

Hi

I want to use FilterOperator.TopN.
Datas come from a dataSet. The filtered column type is Int32
I have this error:   "value of top/bootom filter should evaluate to Integer"

Filter filter1 = new Filter();
filter1.Expression = "=Fields.DAYNUMBER";
filter1.Operator = FilterOperator.TopN;
filter1.Value = "1";

this.table2.RowGroups[0].ChildGroups[1].Filters.Add(filter1);

[Forest]

It's ok.

I have to use : filter1.Value = "=1";