Can you provide the following information for us to better assist you with this issue:
1.) Firmware version currently installed on the AP 541N.
2.) Version of the MacBook you are using.
3.) Wireless encryption type you have setup on the AP 541N.
4.) What is the current version of the Mac OS X system installed on the MacBook?
5.) Have you updated the MacOS X to the latest system udpate?
Thanks,
Chris