Problem with "try-catch" in a web request vb.net - vb.net

Question

I'm making a web request that completes successfully most of the time (target$ is a URL). But occasionally my code throws a valid exception, 404 not found, if the URL target$ doesn't exist, and execution stops. The code:
Sub scrape(target$)
Dim request As WebRequest = WebRequest.Create(target$)
Dim response As WebResponse = request.GetResponse()
Dim dataStream As Stream = response.GetResponseStream()
' Open the stream using a StreamReader for easy access.
Dim reader As New StreamReader(dataStream)
' Read the content.
Dim responseFromServer As String = reader.ReadToEnd()
txtResponse.Text = ""
txtResponse.Text = responseFromServer
' Clean up the streams and the response.
reader.Close()
response.Close()
end sub
The exception, if thrown, happens in the second line, "Dim response...". So I tried adding a "try-catch" as shown.
Sub scrape(target$)
Dim request As WebRequest = WebRequest.Create(target$)
Dim response As WebResponse = request.GetResponse()
Try
Dim dataStream As Stream = response.GetResponseStream()
Catch
exflag = True
End Try
' Open the stream using a StreamReader for easy access.
Dim reader As New StreamReader(dataStream)
' Read the content.
Dim responseFromServer As String = reader.ReadToEnd()
txtResponse.Text = ""
txtResponse.Text = responseFromServer
' Clean up the streams and the response.
reader.Close()
response.Close()
end sub
But now when I try to compile the code, VisualStudio tells me that "datastream is not declared" and the compile fails.
What am I doing wrong and how do I catch the exception when it's thrown?
Thanks...