You probably have seen the popular code for detecting a mobile device from a .NET app. I have seen it is widely used by many developers. However, I haven't seen so far one who mentioned to make sure we have a user agent. Pretty much everyone assumes we always have one. If you use the HttpWebRequest object to send a Url somewhere. On that server, the user agent object would not be initialized.

So, the code is enhanbed like this:

    Public oRequest As System.Web.HttpRequest

    ' This assumes oRequest is initialized before coming here

		Dim laMobileType(66) As String

		cUserAgent = oRequest.UserAgent

		' If this is recognized at the object level
		If oBrowser.IsMobileDevice Then
			lMobileBrowser = True
		Else

			' If this is recognized at the WAP level
			If Not oRequest.ServerVariables("HTTP_X_WAP_PROFILE") Is Nothing Then
				lMobileBrowser = True
			Else

				' If the server variable exists
				If Not oRequest.ServerVariables("HTTP_ACCEPT") Is Nothing Then

					' If this is recognized at the WAP level at this verification
					If oRequest.ServerVariables("HTTP_ACCEPT").ToLower.Contains("wap") Then
						lMobileBrowser = True
					End If

				End If

				' If we have not recognized it yet
				If Not lMobileBrowser Then

					' If this is recognized at the user agent level
					If Not oRequest.ServerVariables("HTTP_X_WAP_PROFILE") Is Nothing Then
						lMobileBrowser = True
					Else

						' If we have a user agent object
						If Not cUserAgent Is Nothing Then

							' Initialization
							laMobileType(1) = "midp"
							laMobileType(2) = "j2me"
							laMobileType(3) = "avant"
							laMobileType(4) = "docomo"
							laMobileType(5) = "novarra"
							laMobileType(6) = "palmos"
							laMobileType(7) = "palmsource"
							laMobileType(8) = "240x320"
							laMobileType(9) = "opwv"
							laMobileType(10) = "chtml"
							laMobileType(11) = "pda"
							laMobileType(12) = "windows ce"
							laMobileType(13) = "mmp/"
							laMobileType(14) = "blackberry"
							laMobileType(15) = "mib/"
							laMobileType(16) = "symbian"
							laMobileType(17) = "wireless"
							laMobileType(18) = "nokia"
							laMobileType(19) = "hand"
							laMobileType(20) = "mobi"
							laMobileType(21) = "phone"
							laMobileType(22) = "cdm"
							laMobileType(23) = "up.b"
							laMobileType(24) = "audio"
							laMobileType(25) = "SIE-"
							laMobileType(26) = "SEC-"
							laMobileType(27) = "samsung"
							laMobileType(28) = "HTC"
							laMobileType(29) = "mot-"
							laMobileType(30) = "mitsu"
							laMobileType(31) = "sagem"
							laMobileType(32) = "sony"
							laMobileType(33) = "alcatel"
							laMobileType(34) = "lg"
							laMobileType(35) = "eric"
							laMobileType(36) = "vx"
							laMobileType(37) = "NEC"
							laMobileType(38) = "philips"
							laMobileType(39) = "mmm"
							laMobileType(40) = "xx"
							laMobileType(41) = "panasonic"
							laMobileType(42) = "sharp"
							laMobileType(43) = "wap"
							laMobileType(44) = "sch"
							laMobileType(45) = "rover"
							laMobileType(46) = "pocket"
							laMobileType(47) = "benq"
							laMobileType(48) = "java"
							laMobileType(49) = "pt"
							laMobileType(50) = "pg"
							laMobileType(51) = "vox"
							laMobileType(52) = "amoi"
							laMobileType(53) = "bird"
							laMobileType(54) = "compal"
							laMobileType(55) = "kg"
							laMobileType(56) = "voda"
							laMobileType(57) = "sany"
							laMobileType(58) = "kdd"
							laMobileType(59) = "dbt"
							laMobileType(60) = "sendo"
							laMobileType(61) = "sgh"
							laMobileType(62) = "gradi"
							laMobileType(63) = "jb"
							laMobileType(64) = "dddi"
							laMobileType(65) = "moto"
							laMobileType(66) = "iphone"

							' For each mobile type
							For lnCounter = 1 To 66

								' If this is one of them
								If cUserAgent.ToLower.Contains(laMobileType(lnCounter).ToLower) Then
									lMobileBrowser = True
								End If

							Next

						End If

					End If

				End If

			End If

		End If