What error are you getting??
The first thing that comes to mind is that you cannot declare an array with a specified size as a structure member. You have to initialize the array in the constructor of the structure, but this is a bit of a hack because you must declare a New with a parameter, even if you don't use the parameter:
Private Structure ResponseFrame
Dim InPtr As Byte
Dim Outptr As Byte
Dim TxBuff(,) As Byte
Dim TxIpAddress() As String
Dim TxPortNo() As String
Dim TxSize As Byte
Sub New(dummy As Integer)
ReDim TxBuff(RESPONSE_BUFF_SIZE, 12)
Now, when you use the Struct, you have to new up an instance of the structure to get its New method to run:
Dim myInstance As New ResponseFrame(0)
The second thing that comes to mind is that RESPONSE_BUFF_SIZE is not visible to the structure. Since it's Private, it's only visible to the container that it's defined in.
The better way around this is to convert the structure to a class since, in order to use it, you'll be treating the structure like a class anyway.