Clean uninstall and reinstall of the SMP agent on the client will solve the issue.
To do this,Go to the location:<Install directory>:program files\altiris\altiris agent
Execute the command : aexagentutil.exe /clean
To reinstall,Go to Action ->agent/plugins->push symantec management agent
Then select the computer and install the agent.
If the plugins install policies are turned on,they will get installed automatically,If not the plugins have to be installed manually.