If it's that old, I'm betting it doesn't use HTTPS for its connections. You could do a network packet capture on the XP machine (or if you can find one, hook it up to a network hub with another computer attached and capture there) while performing the "clear error" action and find out how it works/what you need to send to it to clear the error. You could also set up a SPAN port on a switch and mirror the traffic on the port going to the printer to capture the traffic, if you have a switch capable of doing that. If not, you can get one off Amazon for about $100.

It'd be pretty simple to put together a script that sends the "clear error" action to the printer after seeing how it's done in the packet capture. I've done this numerous times, the latest of which was for a network-connected temperature sensor that I wanted to tie into but didn't (publicly) expose an API of any kind.