No idea, but the net tells me it almost always relates to control / socks port configurations. 
Sometimes gateway connection problems e.g. not fully bootstrapped too.
A previous Tor Browser release e.g. 6.5a4 was blocked with the same error, and Patrick had to play around with anon-ws-disable-stacked-tor to get it working. e.g. see here:
Iām sure one of the experts here will ask: standard Whonix or Qubes-Whonix & what does WhonixCheck say? That might help to identify the problem by running WhonixCheck in verbose mode in both the gateway and workstation (via the terminal).
Also, when you say āclose to default settingsā, maybe something you changed is causing a conflict?
Since Whonix users arenāt reporting problems en masse, it is unlikely to relate to the recent Tor Browser release and some incompatibility with system Tor in Whonix, or some Whonix update bug.
Now Iāll butt out and let one of the experts deal with thisā¦