Check the following :
- Check if your APs are getting an IP address
- How are your APs reaching the controller : DNS, DHCP Option 43, ADP ?
- Make sure your APs can reach the controller (console into the AP and see what's going on) and also make sure that there's no firewalls in between blocking GRE or PAPI
- Make sure that cpsec is not enabled
- do show log system all see there's any particular errors that might indicate why your APs are failing to attach
- Is this a master or a local controller ?
- How's your default AP group configured ?