I am not an ASP or a .NET guy so you can take this with a grain of salt but I feel pretty safe in saying this: you need to have a plan to migrate. MS hasn't said it officially but I suspect ASP is currently in the waiting-for-EOL list as we speak. MS won't kill it (that would be foolishness beyond belief) but they'll just move in a different direction. Even if that move is years away you need to start planning NOW. It wouldn't surprise me to find that Classic ASP stops be available by default for IIS in the not-too-distant future. It already appears that the SDK for Paypal is no longer supported.

Now I understand migration is a scary thing and bosses are stubborn on the issue (It'll cost WHAT?) So then what? What I would highly suggest is that, if you absolutely MUST stay with it for now, that you build your own framework for making calls. My largest gripe with most SDKs is that it does too much for you so you fail to understand how it's doing what it's doing. Many programmers simply rely on it to wipe their chin for them. That's fine until Paypal does something new and suddenly the rug is yanked out from underneath you. The SDK doesn't do that so you're at someone else's mercy. Go into the SDK and pull the nuts and bolts apart. Learn how it works. Build your own calls and send them to Paypal and see what happens. Honestly, you'll be a better developer for it. Paypal could go in any new direction and you can keep up, support or not. Be a pal to the people here, tho, and publish it (the core framework). Community support and all.

In the end you're going to have to do some work on this. Either migrate or do it yourself. If I were you, I wouldn't rely solely on the SDK being kept up-to-date. Those are your options.