Updating an already released web-service elegantly

[24 Vitamins]

I have a SOAP web-service ISAPI and a client application (win32) that
connects to it - both written in BCB6. I connect to the service in the
client app using the WSDL Importer which creates a static binding the
service. I release both apps to users who end up deploying the web-service
themselves on their own network.

In the next release I need to update the web-service with some new
functionality and consume it from the updated client app.

What I am concerned with is the user that gets the update - installs it on
the client and tries to use it without first updating the web-service ISAPI.
I suspect that the client service interface will fail to even bind. Or at
least it will throw an exception when it tries to call a function that does
not exist.

I want to do something like this:

clientapp::Foo()

{

bind to web-service

if (web-service is the old one)

{

prompt user to update the web-service ISAPI first

return;

}

// its definitely the new service

call the new web-service function()

}

I guess I can simply wrap the binding and calling in a try catch and if
there is a soap exception assume it is the old service - but that sucks - it
is an assumption.

What do you suggest?

BCB 6.