Hello Peggy,
Have you tried replacing sylink.xml on the machine?
Try this:-
In SEPM, go to the clients tab and then select a group and right click on the same and select the option of Export Communication settings.
In the file name it should only be sylink.xml and then select the destination and export the same.
Now use this sylink.xml and open the SEP client shield from the System tray and then go HELP and then to TROUBLESHOOTING
Under Communication Settings Click IMPORT and get the Previously imported sylink over here.
After a few minutes the client should communicate.