If the XAMPP installation is running on your personal PC, this is really a bad idea in production. Normally there are all kinds of routers and firewalls between your PC and the blackboard installation.
Anyway, I fixed the link to the old documentation, so, please verify that everything is installed correctly.
The error indicates there is a mismatch between the URL given in the configuration end the URL actully sent buh the software. This can be caused by routerss, proxies, reverse proxies between the blackboard installation and your Xerte install. The blackboard machine should be able to ceonnect to the xerte installation using the smae URL as you use to open Xerte.