Hi Gi0
yes, duplicate IP will cause issues. Presumably these APs (or at least one of them) has a static IP set. Depending you want to change to DHCP or stay with static IP, you need to get a console cable (9600,8,n,1) and connect to the AP serial port.
power on the AP, interrupt the boot sequence, and enter the command "printenv". This will dump all the saved setup on the AP, you will see amongst other things the IP/netmask/default gateway if they are configured.
If you have a static IP you can change it like so:
setenv ipaddr 1.2.3.4
save
boot
or if you want to revert to DHCP, you need to do a blank setenv for each item relating to the IP address, i.e. netmask, ipaddr, gatewayip.
setenv netmask
setenv ipaddr
setenv gatwewayip
save
boot
you can check that dhcp is working by entering "dhcp" command at the same prompt.
regards
-jeff