I have a client XPsp2 with Zen 10.1

When i try to remote control the client I get

"The managed device was unable to initialize the Novel Encryption scheme
for the session...Make sure time sync..."

When I go to the client I get NO fingerprint under Remote Management -.
Security and a message stating this server is not configured with a
valid certificate.

I uninstalled / reinstalled the client agent last time this happened
which worked but it looks like its happening again.

what can i look at? Whys is there no server cert on the client under