指定的转换无效？解决方案

指定的转换无效？
控件中XAML如下：

<UserControl x:Name="Arc_Monitor" x:Class="FN_InventoryMonitor.ArcMonitor"

             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 

             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"

             xmlns:local="clr-namespace:FN_InventoryMonitor"

             mc:Ignorable="d" 

             d:DesignHeight="300" d:DesignWidth="300" Loaded="Arc_Monitor_Loaded">

    <UserControl.Resources>

        <local:PointStartOuter x:Key="PointStratOuter"></local:PointStartOuter>

        <local:PointEndOuter x:Key="PointEndOuter"></local:PointEndOuter>

        <local:PointStartInner x:Key="PonitStratInner"></local:PointStartInner>

    </UserControl.Resources>



    <Grid>

        <Canvas>

            <Path Stroke="Blue" Fill="White" >

                <Path.Data>

                    <PathGeometry>

                        <PathFigure IsClosed="False" StartPoint="{Binding ElementName=Arc_Monitor,Path=ActualWidth,Converter={StaticResource PointStratOuter}}">

                            <ArcSegment x:Name="Arc_Outer" Size="150,150" SweepDirection="Clockwise" IsLargeArc="False">

                                <ArcSegment.Point>

                                    <MultiBinding Converter="{StaticResource PointEndOuter}">

                                        <Binding ElementName="Arc_Monitor" Path="ActualWidth" Mode="OneWay"></Binding>

                                        <Binding ElementName="Arc_Monitor" Path="Percent" Mode="OneWay"></Binding>

                                    </MultiBinding>

                                </ArcSegment.Point>

                            </ArcSegment>

                            <!--<LineSegment Point="180,100"></LineSegment>-->

                            <!--<ArcSegment Point="100,20" Size="80,80" SweepDirection="Counterclockwise" IsLargeArc="False"></ArcSegment>-->

                        </PathFigure>

                    </PathGeometry>

                </Path.Data>

            </Path>

        </Canvas>

    </Grid>

</UserControl>

其中绑定函数如下：

    public class PointEndOuter : IMultiValueConverter

    {

        public object Convert(object[] value, Type targetType, object parameter, CultureInfo culture)

        {

            double width = (double)value[0];

            width /= 2;

            double percent = (double)value[1];


            Point point = new Point((width + Math.Sin(360 * percent / 100) * width), (width - Math.Cos(360 * percent / 100) * width));

            return point;


        }

        public object[] ConvertBack(object value, Type[] targetType, object parameter, CultureInfo culture)

        {

            throw new NotImplementedException();

        }

    }

<Binding ElementName="Arc_Monitor" Path="Percent" Mode="OneWay"></Binding>
这一句中，Percent是自定义的依赖项属性，结果在编译器中就报错“指定的转换无效”，而在其他程序中加载此控件则能正常运行，请问如何解决这所谓的“转换无效”问题？

------解决思路----------------------
Percent 是什么类型的？ 在Converter中 加个断点，看value[1] 的值。