Well, mine is even worse.
It only shows:
HTML Importer
Importing HTML files…
Unfortunately, setting WP_DEBUG and enabling the logger shows nothing
relevant.
@sdavissm: Did you play around with the html tags you can configure in the importer? – and also, did you try to tidy5 your input html?
Hoping Stefanie comes back soon 😉
Hi, I have the same issue.
Tried to tidy the html, I have Version 2.6 of the plugin
on a recent 4.6.1 installation with php 5.6.26.
The Error seems to be independent of the html.
I stay with the state as shown here:

how to debug that?
thanks, George.