Accessing Web Service through a VPN client on the MC70

Hi...
I am developing an application in vb.net which calls a web service hosted on a remote machine conected through a VPN connection.
If I execute my code in a desktop application, (also connected to the same server over VPN) , I receive a positive response from the web service.        
Although when I access the same code through a Pocket PC  I receive a web exception Protocol Error.
I also pass the net credentials of the remote machine when accessing the web service. I still receive this error.
I can also navigate to the webservice using Internet Explorer on the device. So this rules out the exception not being able to call the webservice.
Kindly provide me with any help as to how i may proceed to overcome this issue
Thanks
Sakina