Check the following as one of them would be causing this error in clean access agent:
1)Ensure that clock on the CAM and CAS are synchronized to be less than 5 mins apart.
2) Check all the switch configs to make sure they are good.
3) Check if the vlans are pruned. If they are not pruned then prune vlans as this could be overloading the mac table
4) Check if you have configured managed subnets for all the vlans passing through CAS? If not, could configure it in [Device Management -> CCA
Servers -> Advanced -> Managed Subnets]
Also providing the event Log and CAS log will help us to troubleshoot the issue better.