Web Request Get Response fails on second try - vb.net

Question

I wrote a program that searches for a user name on a web site and downloads the their main html page, finds the link to the next page and downloads that and so on. When I run the program the first time the get response for the search works correctly and the get response for downloading all of html pages works correctly. However, when I do a second search the get response fails for the search. I thought that maybe it was the server only allowing so many searches in a time period but it isn't that. When I close my program and run it again everything works fine again. Why does the get response fail on any attempts besides the initial one? You can't define a web request as new and their seems to be no way of closing a web request once it gets a response to free up resources. Is it because I run the whole process in a background worker? I don't know what's wrong. I always could do as many searches as I wanted to just yesterday...
Here's my code for the search form:
Private Sub FormSearch_Load(sender As Object, e As EventArgs) Handles MyBase.Load
'if the user name is empty then initialize it
If My.Settings.UserName = "" Then
My.Settings.UserName = ""
End If
'if the current url is empty then initialize it
If My.Settings.CurrentURL = "" Then
My.Settings.CurrentURL = ""
End If
My.Settings.Save()
End Sub
Private Sub TextBoxUserName_TextChanged(sender As Object, e As EventArgs) Handles TextBoxUserName.TextChanged
'if the text length of the text box is greater then zero
If TextBoxUserName.TextLength > 0 Then
'enable the search button
ButtonSearch.Enabled = True
Else
'disable the search button and set focus on the text box
ButtonSearch.Enabled = False
TextBoxUserName.Focus()
End If
End Sub
Private Sub ButtonSearch_Click(sender As Object, e As EventArgs) Handles ButtonSearch.Click
'trim the text box of any spaces
My.Settings.UserName = Trim(TextBoxUserName.Text)
'if the user name is not equal to null
If My.Settings.UserName <> "" Then
'set the current url and test if it exists
My.Settings.CurrentURL = "*url here*"
If URLExists(My.Settings.CurrentURL) = True Then
'save the settings
My.Settings.Save()
'return ok for the dialog result and close the form
Me.DialogResult = Windows.Forms.DialogResult.OK
Me.Close()
Else 'cannot find the account
'set the text box text to null and set focus on it
TextBoxUserName.Text = ""
TextBoxUserName.Focus()
End If
End If
End Sub
Private Function URLExists(url As String) As Boolean
'create a new uri
Dim uriURL As New Uri(url)
'create a new web request of the uri
Dim wrRequest As WebRequest = WebRequest.Create(uriURL)
'set the web request timeout and method
wrRequest.Timeout = 30000
wrRequest.Method = "GET"
'create a new web response
Dim wrResponse As WebResponse
Try
'if the response succeeds then return true
wrResponse = wrRequest.GetResponse
Return True
Catch ex As Exception 'the response failed so return false
LabelMessage.Text = ex.Message
Return False
End Try
End Function