Hi,
See below for understanding about the management vlan of IAP
1) By default IAP's management traffic (interface E0) is sent out untagged
2) Since the traffic is untagged, the switchport on switch can be configured with IAP management vlan in 2 ways (assuming you didnt change the value in uplink vlan in individual IAPs)
a) Native Vlan
b) access port
3) So in your case, you need to check what is the status of your switch's port? you can determine the IAP management vlan basically from the switch
4) Since you are not able to ping, but you were able to ping i believe you had DNS working for you. Since if IP address assignment is set to virtual controller assigned, then all the traffic from guest IPs is Nat'd to E0 ip.
So can you check which vlan IAP belongs to now?