App cant connect to Internet when running on a network - Is this a proxy or Firewall?

[experience]

Hi, one of my clients is running my exe app from a network PC and its throwing an error showing no internet connection

Could a proxy server be blocking it or is this more likely the companies firewall?

When my software starts it checks if there is an internet connection using the following:

 Public Function IsConnectionAvailable(ByVal site As String) As Boolean
        If site = "Y" Then
            site = "http://www.mysite.com"
        End If
        Dim objUrl As New System.Uri(site)
        Dim objWebReq As System.Net.WebRequest
        objWebReq = System.Net.WebRequest.Create(objUrl)
        Dim objResp As System.Net.WebResponse

        Try
            objResp = objWebReq.GetResponse
            objResp.Close()
            objWebReq = Nothing
            Return True
        Catch ex As Exception
            objWebReq = Nothing
            Return False
        End Try
    End Function