WPF disable button with IDataErrorInfo

Question

I found this tutorial and I was able to implement it.

How can I disable a button when an errors occurs?

I searched a lot over the net, but I can't find a piece of code that resembles mine. (Yes, I know there about a zillion threads about this matter, but I just don't understand it.)

Here is my current code, it's a bit lengthy:

Public Class GradeVm
    Implements IDataErrorInfo

    Public Interface IDataErrorInfo
        Default ReadOnly Property Item(columnName As String) As String
        ReadOnly Property [Error]() As String
    End Interface

    #Region "Properties"
    Property Grade As Integer
    Property Adjust As Integer
    #End Region

    Public ReadOnly Property [Error] As String Implements IDataErrorInfo.Error
        Get
            Return "Error"
        End Get
    End Property

    Default Public ReadOnly Property Item(columnName As String) As String Implements IDataErrorInfo.Item
        Get
            Select Case columnName
                Case "Grade"
                    If IsNumeric(Me.Grade) = False Then
                        Return [Error]
                    End If
                Case "Adjust"
                    If IsNumeric(Me.Adjust) = False Then
                        Return [Error]
                    End If
            End Select

            Return ""
        End Get
    End Property
    End Class

Answer 1

This combined with the code here did the trick! Finally!! :)