1. Don't use CrystalReportViewer1.RefreshReport or CrystalReportViewer1.Refresh
2. Set Report source from properties to none
3. Report source must be assigned Dynamically
4. in your code have this sequence
REPORT1.Refresh()
REPORT1.SetParameterValue(0, "some default value")
CrystalReportViewer1.ReportSource = REPORT1