Your user's version of Desktop is not seeing the CAL, so it is running as Personal Edition. It might be that his user name has changed in some way (or some underlying AD changes have affected the license lease) or that he is not connecting to the server to renew the license lease and now the lease has expired.
This lease is normally renewed automatically but he may need to use File | Open In Server to open a server session to get the lease renewed manually.
Thanks for your quick reply. If he does open in server then he gets:
Failed to reach server...
Connected to server OK, security settings denies access
If he access via browser, he can access the file, which means he can access the server right?
What can be the problem then? which security settings should we check?