Your manager sounds like he has abandoned management by objectives and replaced it with management by clichÈ. Statements such as the "weak link in the chain" or "shape up" are not effective pieces of feedback. For feedback to be useful, it should be provided as close to an employee's behavior as possible, and it should be clear, specific, and based on performance. And further, your manager should have worked with you to develop an action plan to correct the problem.
On a broader basis, employees should never be surprised by information that their manager provides during a performance review. It is the manager's job to give the employee with feedback, guidance, and coaching on a regular basis, as this is the best way for an employee to learn, grow, develop, and improve on the job.
At this point, you should ask your manager for more specific information as to the problems that he sees in your performance, along with his suggestions regarding the kinds of steps that you should take in order to correct them. At the same time, you should also ask him to provide you with more feedback and guidance along the way. The irony is that he sounds like the weak link that needs to shape up.
| 
