I just copied your code and I am going to test this in my application to see what is happening.
Tim

>
>I've tried it like this, but I still get the same error :(
>
>Here's my actual code:
>
>in my PolicyRider.Partial.cs:
>
>

        public string ValidateSumAssuredMaxMin(Guid? planPK, decimal? sumAssured)
>        {
>            // Get the Plan for the specified PlanPK
>            Plan oPlan = new Plan();
>            oPlan.GetPlanByPlanPK((Guid)planPK);
>
>            // Call the validate method in the Rules object
>            return this.Rules.ValidateSumAssuredMaxMin(sumAssured, oPlan.Entity.MinSumAssured, oPlan.Entity.MaxSumAssured);
>
>        }

>
>In my PolicyRiderRules.Partial.cs:
>
>

        public string ValidateSumAssuredMaxMin(Decimal? sumAssured, Decimal? min, Decimal? max)
>        {
>            string message = null;
>            // check that the sum assured meets the min and max sum assured requirements
>            if (min > (Decimal)sumAssured
>                    || max < (Decimal)sumAssured)
>            {
>                message = "Rider Sum Assured must be between " + min.ToString() + " and " + max.ToString();
>                this.AddErrorProviderBrokenRule("SumAssured", message);
>            }
>            return message;
>        }

>
>In my PolicyEdit.aspx.cs:
>
>

        protected void txtRiderSumAssured_TextChanged(object sender, EventArgs e)
>        {
>            TextBox thisTextBox = (TextBox)sender;
>            this.oPolicyRider.Rules.ClearAll();
>            GridViewRow gvr = (GridViewRow)thisTextBox.Parent.Parent;
>            if (this.oPolicyRider.ValidateSumAssuredMaxMin((Guid)this.oPolicyRider.DataSet.Tables[0].Rows[gvr.RowIndex]["RiderFK"], decimal.Parse(thisTextBox.Text)) != null)
>            {
>                // show the message somehow
>            }
>
>            this.CalculateRiderPremium(true, gvr);
>            this.SetFocus(gvr.Cells[3].Controls[1]);
>        }