I encounter an issue with the XamDataGrid custom filter dialog.   I have a very simple XamDataGrid defined something like below.   Note that I enable record filtering by setting  AllowRecordFiltering="True"

 <igWPF:XamDataGrid Name="xdg" DataSource="{Binding}"
                           >
            <igWPF:XamDataGrid.FieldSettings>
                <igWPF:FieldSettings
                    AllowEdit="False" 
                 LabelClickAction="SortByMultipleFieldsTriState"
                 LabelTextAlignment="Center"
                 LabelTextWrapping="Wrap"
                 CellClickAction="SelectRecord"
                AllowGroupBy="False"
                AllowRecordFiltering="True"
                AutoSizeScope="AllRecords"
                AutoSizeOptions="All"/>
            </igWPF:XamDataGrid.FieldSettings>
        </igWPF:XamDataGrid>

So when I work on a numeric column and build a custom filter using the custom filter dialog. I follow the following steps.

a) Add a new condition. Select the "Bottom" operator. Do nothing.

b) Add another condition.  The "Equal" operator is selected by default.   Note that the first condition (Bottom operator) does not show an error message. 

c)  Remove the second condition.   Note that the dialog only remains one condition, i.e. "Bottom".   The condition is in an error state, i.e. no operand, but no error message is shown in the third column.

d) Close the dialog by clicking "ok"

e) Now there is an invalid condition applied to the column.   The clear condition icon is shown.

f)  When the user clicks the "clear condition" icon, an "ArgumentException was unhandled" is thrown saying, "Invalid operand value.  It must be a number."

This looks like a bug for the validation codes in the  custom filter dialog.