Roaming Profile error

We have a computer lab with about 25 PCs set up with roaming profiles. I’d say about 10 of them receive this error message when logging in:

Your roaming profile is not available. You are logged on with the locally stored profile. Changes to the profile will not be copied to the server. Possible causes of this error include network problems or insufficient security rights. If this problem persists, contact your network administrator.

I have checked user permissions and they match the ones that do work. Anybody have any experience with this error and can help me out?

Thanks