I'm using SSRS 2008 R2. I need to get a count of child records to a parent. Within scope of the parent, I tried the following call: =Count(LookupSet(Fields!ID.Value, Fields!ActivityID.Value, Fields!ActivityID.Value, "ChildDataSet")) thinking this would give me a count of records in the array of values returned from the child dataset (ChildDataSet). But I get this error: Warning 3 [rsAggregateOfInvalidExpressionDataType] The Value expression for the textrun ‘Textbox28.Paragraphs[0].TextRuns[0]’ uses an aggregate function with an expression that returned a data type not valid for the aggregate function. What am I doing wrong? How can I get a count of the children in the scope of the parent? Thanks in advance.

LookupSet returns an array of items so you cannot simply count them You will most likely need to pass the result of the lookupset to a custom code function such as: Function CountItems(varArray as array) as integer Dim RetVal as integer RetVal = ubound(varArray) + 1 Return RetVal End Function Call it like: =code.CountItems(LookupSet(Fields!ID.Value, Fields!ActivityID.Value, Fields!ActivityID.Value, "ChildDataSet"))Rgds Geoff