If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. As the name already tells you, 'WriteByte' expects a single Byte and not a String (TextBox2.Text). Convert TextBox2 to a Byte array first and then use 'Write' to write the Byte array to the correct position.
Something like this. Replace the 0 in Seek with the correct offset.

Dim byteArray() As Byte = System.Text.Encoding.UTF8.GetBytes(TextBox2.Text)
 
Using fs As New FileStream("filepath", FileMode.Open, FileAccess.Write)
    fs.Seek(0, SeekOrigin.Begin)
    fs.Write(byteArray, 0, byteArray.Length)
End Using

Then use the function below. Make sure that the Hex string has an even number of characters or an exception will occur.

Imports System.Runtime.Remoting.Metadata.W3cXsd2001
 
Private Function HexStringToByteArray(ByVal hex As String) As Byte()
    Dim shb As SoapHexBinary = SoapHexBinary.Parse(hex)
    Return shb.Value
End Function
 
Dim byteArray() As Byte = HexStringToByteArray(TextBox2.Text)
 
'// other code

Private Function ByteArrayToHexString(ByVal byteArray As Byte()) As String
        Dim hex As New System.Text.StringBuilder(byteArray.Length * 2)
        For Each b As Byte In byteArray
            hex.AppendFormat("{0:x2}", b)
        Next
        Return hex.ToString()
    End Function
 
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim byteArray(15) As Byte
 
        Using fs As New FileStream("filepath", FileMode.Open, FileAccess.Read)
            fs.Seek(0, SeekOrigin.Begin)
            fs.Read(byteArray, 0, byteArray.Length)
        End Using
 
        Label5.Text = ByteArrayToHexString(byteArray)
    End Sub

::Edit::
You should probably use "Dim byteArray(7) As Byte", as 8 Bytes will give you a Hex String of 16 characters. Advertiser Disclosure: Some of the products that appear on this site are from companies from which TechnologyAdvice receives compensation. This compensation may impact how and where products appear on this site including, for example, the order in which they appear. TechnologyAdvice does not include all companies or all types of products available in the marketplace.