When an IAP is converted to a CAP, the ip address you pointed it to is provisioned into the CAP and it always points to that address, unless you change it. If it can no longer find the controller, you must either:
1 - Get into the CAP using a console cable and stop it at the "apboot" prompt and change the master to the new address by doing:
setenv master <new master ip address>
save
boot
or:
2 - Using the reset button and then converting it to a CAP again using the new VRRP address.
Only plug in the AP in using ethernet0.