Most likely you are getting hit by the "User-Agent" string validation which by default will block anything that does not pretend well enough to be a normal web browser.
I already sent Ken a support request asking to skip those new validation functions for local/LAN addresses as that should resolve the majority of 3rd-party integration issues. But unless Ken walks back this entire set of security features, you can expect it to continue causing pain when accessing via an address which Blue Iris does not recognize as local.