I am very familiar with what needs to be updated for PHP, but I'm honestly not sure if paypal even supports ASP Classic with their new system.
My guess is that eventually they won't and there won't be anything anybody can do for you, so you'll have to switch to php or .NET if you are sold on the Microsoft platform, and whatever you switch to, WebAssist will only be providing solutions and extensions in PHP moving forward.
I may not know the exact lines in our code, but I'm trying to explain to you how to fix your problem, and the way you would start is you would look up the code from paypal that you need to integrate into your eCart code.
The next step would be to find and integrate it into the eCart, and you have to attack these things sequentially if you want to get them done.
I know you don't want to delve into the code, but unfortunately your options with using ASP classic are that you are going to have to from now on if you want to make updates that aren't included. This will include updating to new versions of payment gateways or shipping providers. The long term answer to continue using WebAssist tools and support is to move to PHP.