Update failed: The anime (id: ***) is already in the list.

[IO5]

Happened to my in a place with really bad internet connection. My local and MAL database got somehow desynched, which is fine with connection this unstable.
What isn't fine is the fact I get this error message every damn time Taiga connects to the server.
I fixed the problem manually by removing offending line from history.xml queue, but Taiga should do that automatically.

[erengy]

The underlying cause for this issue is fixed in v1.2.5, but I decided not to make Taiga ignore a legitimate error. Please see #328 for more information.

Note that you could have deleted the offending anime from Taiga's update queue at History page too; no need to edit the history.xml file directly.