WSUS - Server not pushing updates to clients - Clients are listed as NOT YET REPORTED

Hi

We are facing problem with WSUS Server.

It is listing all the client systems but only some are showing as 99% updated and other are showing as "NOT YET REPORTED"

We have about 100 systems which are showing the same.

We are able to get all the information but unable to update them.

Please guide

Thanks

Naveen