You may want to review the criteria used for Compliance - the VSE and Agent Compliance dashboard is based on the criteria : of DAT version being within 3 revisions old of the master repository, and Virusscan being 8.5 or above. Additionally, agent is version 3.6 or above.
Check if the machines which fall under the non-compliant list satisfy these criteria. you can edit the query to check if youu have specified a different criteria that may be causing systems to be flagged as non-compliant (for e.g.DAT not older than 2 revisions?).
Also check if clients are able to communicate with ePO and are successfully updating the properties - DB\Logs\server.log can provide some clues if there is any failure in agent communication.
Thanks for the reply, but it turned out to be the agent key updater as i suspected.