Protx Intergration(VSP Direct) with VB.NET

[BODAR77]

I was hoping that someone can help me with a problem. I am trying to link my
web-site to the Protx payment system using VB.NET and Protx's VSP DIRECT. I
have downloaded the .Net kit that protx supply and have referenced the
protx.vb.dll and imported protx on my checkout.aspx.vb
when I click submit to send the relevent details as a string
I get this error.

Server Error in '/' Application.

Object reference not set to an instance of an object.

Description: An unhandled exception occurred during the execution of the
current web request. Please review the stack trace for more information
about the error and where it originated in the code.

Exception Details: System.NullReferenceException: Object reference not
set to an instance of an object.

Source Error:

An unhandled exception was generated during the execution of the current
web request. Information regarding the origin and location of the
exception can be identified using the exception stack trace below.

Stack Trace:

[NullReferenceException: Object reference not set to an instance of an
object.]
Protx.Vsp.VspTransaction..ctor(String version, VspServiceType
serviceType, VspTransactionType txType, String vendorTxCode) +75
Protx.Vsp.DirectTransaction..ctor(String vendorTxCode,
VspTransactionType txType) +25
e_productdirect.Checkout.placeOrderButton_Click(Ob ject sender,
EventArgs e) in C:\e-productdirect\Checkout.aspx.vb:188
System.Web.UI.WebControls.Button.OnClick(EventArgs e) +108
System.Web.UI.WebControls.Button.System.Web.UI.IPo stBackEventHandler.Rai
sePostBackEvent(String eventArgument) +57
System.Web.UI.Page.RaisePostBackEvent(IPostBackEve ntHandler
sourceControl, String eventArgument) +18
System.Web.UI.Page.RaisePostBackEvent(NameValueCol lection postData)
+33
System.Web.UI.Page.ProcessRequestMain() +1292

Version Information: Microsoft .NET Framework Version:1.1.4322.2300;
ASP.NET Version:1.1.4322.2300

It refers to this line of code:
Dim tx As New Protx.Vsp.DirectTransaction(vendorTxCode,
Protx.Vsp.VspTransactionType.Payment)

Its really got me stumped can anyone help.