Since updating XAP within the last month I've been getting "Object reference not set to an instance of an object." errors. I've uninstalled, reinstalled and restarted Windows 8.1 machine a lot of times. I suspect the issue is related to VirtualBox Host-Only Ethernet Adapter #2. The IPv4 adapter address is 0.0.0.0 and I'm unable to set it manually to 10.71.34.1. When I try setting it through Network and Sharing, it tells me that my Hyper-V Virtual Ethernet Adapter is using that address. I need Hyper V for Windows simulators, and before updating XAP recently, I was able to keep Hyper-V on and run XAP no problem. Disabling the Hyper V service does not fix my issue.
More strange behavior - Every time I attempt to run one virtual device, XAP creates another VirtualBox Host-Only Ethernet Adapter #3, 4, 5, 6, 7... all of them have IPv4 address as 0.0.0.0. I mention this only because it seems most people don't have so many adapters for a single virtual device. Honestly, when it worked I never opened VirtualBox to see what good network preferences look like. I attempted to set IPv4 address to 10.71.34.3, as a test, and it gives me a different error message "Failed to Initialize Device", and it does not create an additional adapter for each attempt. I think i'm on to something, but I may be going down the wrong path to fix this.
I've attached the bug report.