UDF To Return Value To Cell

In formula bar I will be having my own custom function (for eg: =yieldCurveGetData(RTD(".......")) which is invoking VBA macro,In the macro I will be having the below code which is should display the value '123' or the string value.But foreach statement is not executing it's is terminated after " Range(rCell.AddressLocal) = 123 'arrayData ".

Function yieldCurveGetData(arrayData As String) As Variant
Dim rCell As Range
Dim msgVal As String
For Each rCell In Selection
Range(rCell.AddressLocal) = 123 'arrayData
msgVal = msgVal & vbCrLf & rCell.AddressLocal & " = " & rCell
Next rCell
MsgBox msgVal
End Function

Iam not sure what's going wrong in it.Because the same function I triggered thru a button It's working. In the above function I checked for "Selection.Count" and it's returning seletion count correctly.