求计算天数的函数的正确使用方法

Dim i As Integer
With VSFlexGrid1
  For i = 1 To .Rows - 1
  If .TextMatrix(i, 9) <> "完成" Then
     .TextMatrix(i, 4) = DateDiff("d", .TextMatrix(i, 3), DTPicker1.Value)
  End If
  Next i
End With

红色部分会报错（13，类型不匹配），求此函数的正确使用方法
[最优解释]
.TextMatrix(i, 3) 的内容是什么？

试试 .TextMatrix(i, 4) = DateDiff("d", CDate(.TextMatrix(i, 3)), DTPicker1.Value)
[其他解释]
Dim i As Integer
With VSFlexGrid1
For i = 1 To .Rows - 1
If .TextMatrix(i, 9) <> "完成" Then
.TextMatrix(i, 4) = DateDiff("d", .TextMatrix(i, 3), DTPicker1.Value) <=========这一行会报错
End If
Next i
End Wit