Some of my computer are not downloading updates from the symantec endpoint protection manager.
have you checked if the clients are able to communicate to the SEPM? enable the sylink log on the machine thats not updated and review if it shows any error.
Download and run the SymDiag tool on one of the affected clients to do additional error checking.
In the SEPM do you see green dot on those affected computers? If yes, make sure SEPM policy number and SEP client policy number is the same.