Warning: ignoring param 'title' for book as it is not valid. Possible values are ''.

Symptom:

You are getting the following warning message:

ignoring param 'title' for book as it is not valid. Possible values are ''.

It means that the title param is not set for your content type(e.g. book).

Solution:

  1. Go to admin/config/content/formats and click on the configure link of your text format(e.g. Filtered HTML).
  2. Under Filter settings, click on Link Node.
  3. For each content type, enter the parameters that are allowed.(e.g. title).