I found a compromise solution for my problem. The StartDate and EndDate parameters must be selectable by a calendar-picker. In this case I cannot compute them (in Avaliable Values box) because the SSRS put them in a drop-down list and I do not want this. I decide that in case of StartDate>EndDate the report must run but only on EndDate value (meaning between EndDate and EndDate) and I must show an error message to the User in the parameters bar, before the report runs. So, except the StartDate and EndDate parameters I need another two parameters: XDateStart (as Date) that keep the forumla: IIF(Parameters!StartDate.Value>Parameters!EndDate.Value,Parameters!EndDate.Value,Parameters!StartDate.Value) both in Default and Avaliable values section, parameter I can provide to the DataSet, and XMessage (as Text) parmeter: IIF(StartDate>EndDate,"StartDate>EndDate, Report runs only for EndDate = "+CDATE(FormatDateTime(Parameters!EndDate.Value,FormatDateShort)),"none") that will be automatically updated at every change of the StartDate value, before the report runs. In this manner, the user see the message in parameters bar. I think is a resonable solution.