Eclipse won't start, log error says: ObjectNotFoundException: Tree element

For this issue I had to delete the .snap file located in the directory :

<workspace-directory>\.metadata\.plugins\org.eclipse.core.resources

After deleting that file, I was able to start my Eclipse with no problem.

Recommended: Delete <workspace-directory>\.metadata\.plugins\org.eclipse.core.resources\.snap. This will not reset your workspace and your other projects won't get deleted (as answered by krishna).

Not Recommended: Alternatively, delete the the whole <workspace-directory>\.metadata directory from your workspace and restart.This will reset your workspace and delete all your existing projects in it.

Ran into this error.

There was no .snap file in my .metadata folder.

I had to delete this:

<workspace>/.metadata/.plugins/org.eclipse.core.resources/.root/d+.tree

d+=> some number.

Then I had to re-import the projects and re-assign the working sets. I preferred it over opening a new workspace and redoing settings.