Layout Editor can't add some module block.

[joebordes]

I tried in my install and in the online demo and To Dos appear in both for Campaigns. Review your language files as I suppose that the fact that there is a row with no translation could indicate that something is wrong in those files.

Also, right click on the list and see if the empty row has a value of cbCalendar.

Note that it is also very odd to see Campaigns in that list. I don't think that relations with the same module will work.