Hi.
Please don't bump the posts, it's not allowed.
Also what i am suggesting is you should put some breakpoints
(http://www.startvbdotnet.com/forms/debug2.aspx) and see where the program get's the error.
Having said that, change your sendArp function to this
Code:
Declare Function SendARP Lib "iphlpapi.dll" (ByVal DestIP As UInt32 _
    , ByVal SrcIP As UInt32, ByVal pMacAddr As Byte(), ByRef PhyAddrLen As Integer) As Integer
.
I was going to ask before if you where using API but now it's clear.The problem may be that you have not specified a function correct or use it in the wrong way.But without telling us where exactly you get the error we can only make speculations.