Ask questions

Always ask questions!
When a project is not progressing or an employee does not perform....,
ask questions, direct questions.
We (the Dutch people at least) have the habit to find out through others and trough circumstances to identify what the problem is.
But it is much easier just to ask the person or the project leader what the problem is. If you get an unsatisfactory answer, appeal to the higher goal, and demand that you want to know.
If you got further resistance appeal to your function and responsibilities and his function and responsibilities. Do not threat but push a bit and give it a day to react. Do not come to a situation that you say 'if you do not deliver it, then....'. That is only a very last solution. In that case you can say goodbye to the loyalty of the employee.