I'm having a problem using a X509 certificate for authentication.  I am using
a remote web service, via a web service proxy class (Visual Studio generated,
given the WSDL).  I access the cert and add it to the ClientCertificates
property of this proxy.  This all works fine.

When I first start up, I am prompted by a dialog box informing me that I am
"Signing data with your private exchange key!" and that "An application is
requesting access to a Protected item.", and finally a request for a
password.  This is all fine and desired behavior.

After a few minutes however, I am prompted by a second dialog box just like
above.  And then a few minutes later,  I am prompted again.   And then on and
on.  I am making multiple calls to the web service but the program is using
the same, initial web service proxy instance (which has the cert already
loaded) so I am not sure why I keep getting prompted.  Just to reiterate, the
first dialog box is desired, the others are not.  

If anyone has any suggestions on how to get rid of the extra prompts they
would be much appreciated.  I've been pouring over forum posts for any help
and it seems like a lot of people have the same question but no verified
solution.  I would rather not use the Win32 api but that is a last resort.  
My environment is as follows:

OS:  win2k
.Net:  1.1
Language:  C#
Web Server:  WebLogic

thanks,
Keith