Hexadecimal values cannot be included in a name VB.NET

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VB

XML

I'm trying to write a code to insert items in exist xml file ,I want the items in file to be like this:

<item>
  <title><![CDATA[any title]]></title>
  <link>http://any link</link>
  <pubDate>any date</pubDate>
  <guid isPermaLink="true">any link</guid>
  <description><![CDATA[any description]]></description>
        <media:credit role="author"><![CDATA[any author]]></media:credit>
  <media:category><![CDATA[any category]]></media:category>
  <media:content url="http://any link" height="266" width="127" /> 
  <media:thumbnail url="http://any link" height="266" width="127" />
</item>

so I have write this code :

Dim FilePath As String
        FilePath = "C:\Users\MONZER\Desktop\Karary Web Site\WebApplication1\XMLFile1.xml"
        Dim document As New XDocument
        If File.Exists(FilePath) Then
            document = XDocument.Load(FilePath)
        Else
            Label1.Text = "not done"
        End If

        Dim root = New XElement("item")
        Dim title = New XElement("title", "<![CDATA[" & TextBox3.Text & "]]>")
        Dim link = New XElement("link", TextBox6.Text)
        Dim pubDate = New XElement("pubDate", DateTime.Now.ToString("yyy/MM/dd HH:mm"))
        Dim description = New XElement("description", TextBox5.Text)
        Dim author = New XElement("media:credit",
                                      New XAttribute("role", "author"),
                                      New XAttribute("><![CDATA[", TextBox5.Text + "]]>"))

        root.Add(title, link, pubDate, description, author)
        document.Root.Add(root)
        document.Save(FilePath)
        Label1.Text = "done"

    End Sub

I got this error :
The ':' character, hexadecimal value 0x3A, cannot be included in a name.

What I have tried:

define ab as xnamespace
ab="media:credit" then use it like :
Dim author = New XElement(ab.tostring,
New XAttribute("role", "author"),
New XAttribute("><![CDATA[", TextBox5.Text + "]]>"))
but did not work either!