I feel your pain. I struggled for 2 days trying to get SparkWeb to work even without a firewall.
I had the same error, but it was with every username/password attempt.
It sounds like it may be only finding the admin account??
Here’s what worked for me:
I edited the SparkWeb.html file with the following settings:
I have heard of people getting it to work right out of the box, even with the connectionType = socket and port = 5222.
Let’s hear more…