Parent task translation missing: en, activerecord, errors, models, issue, attributes, parent_issue_id, not_a_valid_parent

Problem
You get the following error in redmine when trying to update a task that has a parent task.

Parent task translation missing: en, activerecord, errors, models, issue, attributes, parent_issue_id, not_a_valid_parent

Solution
It seems that for some reason when you add more than one subtask, the lft and rgt id numbers are not created correctly so you cannot update the subtasks.
If the numbers are overlapping (rgt for first subtask 2 and lft for second subtask 2), then there is a problem.
So in order to be able to solve that you will need to change the lft, rgt ids to have subsequent numbers as:
first subtask: lft -> 1 , rgt -> 2
second subtask: lft -> 3, rgt -> 4

ERD diagrams in Ruby on Rails

Problem

You would like to have an ERD diagram of your database in your Ruby on Rails project.

Solution

You can install the Rails ERD from here, and install it by following the instructions.
For Ubuntu/debian systems should be:

sudo apt-get install graphviz

and then adding the gem to your Gemfile in the development section as:

group :development do
  gem "rails-erd", "~> 0.4.5"
end

You can then run bundle install to install the gem and rake erb to create the diagram pdf.