Paginated reports

[Phaneendrababu]

I'm using two datasets in the paginated report but i'm creating the expression in the textbox by using the Dataset1 only 
expression is 

COUNT(IIF( month(Fields!NextFollowUpDate.Value)<month(today()) and year(Fields!NextFollowUpDate.Value)=year(today()), Fields!LastName.Value, NOTHING))(Fields!LastName.Value, "DataSet1")
If i run this expression I'm getting error like (The 'Value' expression for the textrun 'Textbox18.Paragraphs[0].TextRuns[0]' has a scope parameter that is not valid for an aggregate function. The scope parameter must be set to a string constant that is equal to either the name of a containing group, the name of a containing data region, or the name of a dataset).

[dobregon]

@Phaneendrababu normally the paginated reports or SSRS doesnt work with the aggregation and after that a countif.

Your dataset1 is from SQL or from PowerBI dataset? in both cases, my recomendation is to create a new dataset that it is aggregated with all the conditions that you need. it is not efficient but it works