Regarding the error message "Failed to create view: org.eclipse.mylyn.tasks.ui.views.tasks", here is what happened in my case and how I solved it:
I had this problem with the version of Eclipse Neon (not Luna / Mars), i.e. an error message appeared in the Task List view every time I started Eclipse, even if I used "-no-activate-task" on the command line.
The problem was most likely that I used a "custom" environment created with previous versions, and let Neon adapt it on first launch.
After I created a new โcustomโ environment from scratch, the error went away.
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