Does this happen in both the Project Center views and the Project views? If that's the case, then the projects are saved but not published. Make sure your Project Managers are publishing the projects and not just saving them.
This also happens sometimes with imported projects. In this case, republish the project; that is, use the "Republish assignments" options, not only the "Publish all".
If the issue is only with the Project views and not in the Project Center views, then there is a problem with the publication process. There is an article in the Microsoft Knowledge base (article 810596) that address this specific problem. We have seen that the most common causes are a DSN corrupted, damaged, or changed, wrong permissions to the ViewDrop folder, and the Views Notification Service stopped or blocked.
Finally, if you can restart the server, do so. It's amazing how effective a simple server restart could be!
Greetings.
