When i executed this code, i receive :

System.FormatException: Input string was not in a correct format.

Plz, help me to fix this problem.
Thanks.

Sub DeleteSelectedFile_Click(sender As Object, e As EventArgs)
For Each row As GridViewRow In userFileGridView.Rows
Dim cb As CheckBox = row.FindControl("FileSelector")
If cb IsNot Nothing AndAlso cb.Checked Then

Dim strGUID As String = row.Cells(0).text
Dim idGuid as Guid = New Guid(strGUID)
result.Text=DeleteFile(idGuid)
End If
Next
End Sub


Function DeleteFile(ByVal id As System.Guid) As Integer
       Dim connectionString As String = "Server=10.178.2.38;uid=sa;pwd=veryeasy;database=F iles"
        Dim sqlConnection As System.Data.SqlClient.SqlConnection = New System.Data.SqlClient.SqlConnection(connectionStri ng)

        Dim queryString As String = "DELETE FROM [Files] WHERE ([Files].[id] = @id)"
       Dim sqlCommand As System.Data.SqlClient.SqlCommand = New System.Data.SqlClient.SqlCommand(queryString, sqlConnection)

       sqlCommand.Parameters.Add("@id", System.Data.SqlDbType.UniqueIdentifier).Value = id

        Dim rowsAffected As Integer = 0
        sqlConnection.Open
        Try
            rowsAffected = sqlCommand.ExecuteNonQuery
        Finally
            'sqlConnection.Close
        End Try

        Return rowsAffected
    End Function