求指导，用AddExtrudedSolidAlongPath创建实体失败

Sub Example_AddExtrudedSolidAlongPath()
    ' 该示例将面域沿样条曲线所定义的路径拉伸成实体。
    ' 面域是由圆弧和直线创建的。
    
    Dim curves(0 To 1) As AcadEntity
    ' 定义圆弧
    Dim centerPoint(0 To 2) As Double
    Dim radius As Double
    Dim startAngle As Double
    Dim endAngle As Double
    centerPoint(0) = 5#: centerPoint(1) = 3#: centerPoint(2) = 0#
    radius = 2#
    startAngle = 0
    endAngle = 3.141592
    Set curves(0) = ThisDrawing.ModelSpace.AddArc(centerPoint, radius, startAngle, endAngle)
    
    ' 定义线
    Set curves(1) = ThisDrawing.ModelSpace.AddLine(curves(0).startPoint, curves(0).endPoint)
        
    ' 创建面域
    Dim regionObj As Variant
    regionObj = ThisDrawing.ModelSpace.AddRegion(curves)
    
    ' 定义拉伸路径(样条曲线对象)
    Dim splineObj As AcadSpline
    Dim startTan(0 To 2) As Double
    Dim endTan(0 To 2) As Double
    Dim fitPoints(0 To 8) As Double
    
    ' 定义样条曲线对象
    startTan(0) = 10: startTan(1) = 10: startTan(2) = 10
    endTan(0) = 10: endTan(1) = 10: endTan(2) = 10
    fitPoints(0) = 0: fitPoints(1) = 10: fitPoints(2) = 10
    fitPoints(0) = 10: fitPoints(1) = 10: fitPoints(2) = 10
    fitPoints(0) = 15: fitPoints(1) = 10: fitPoints(2) = 10
    Set splineObj = ThisDrawing.ModelSpace.AddSpline(fitPoints, startTan, endTan)
    
    ' 创建实体
    Dim solidObj As Acad3DSolid
    Set solidObj = ThisDrawing.ModelSpace.AddExtrudedSolidAlongPath(regionObj(0), splineObj)
    ZoomAll
    
End Sub