The error "Parent task is invalid" appears in Redmine and the parent task cannot be set

Created on 2015-11-27 •

MAEDA Go

This article is for Redmine 3.2 or earlier. In Redmine 3.3.0, the problem shown as an example was fixed, and you can now set the same parent task later for issues that have a relation to each other (#13654).

When you try to set an issue as the parent task, the error message "Parent task is invalid" may appear as shown in the figure below.

Example of a situation in which the error message appears

The error "Parent task is invalid" appears when you try to set the same parent task for issues that have a "Related issues" setting to each other, such as "Related to" or "Blocked by".

For example, as shown in the figure below, when "issues #501 and #502 are a parent task and a subtask" and "issues #502 and #503 are related issues", an error occurs if you try to set issue #501 as the parent of #503.

Solution

If you remove all "Related issues" settings between the issues that should have the same parent task, you can set the parent task. After that, set the "Related issues" again.

For example, in the state shown in the figure above, if you remove the relation between issues #502 and #503, you can set #501 as the parent of issue #503 as well. After this, set issues #502 and #503 as related issues again.

How to remember the solution

The cause of the error is easy to understand if you compare issues to people and "Related issues" to "siblings". People do not become siblings first and then get a parent. They are siblings because they have the same parent. In the same way that a parent and a child cannot be siblings, if you set issues in a parent and subtask relationship as related issues, a different error, "This relation would create a circular dependency", appears.