Hi Anthony I don't believe anybody will be able to explain or help you troubleshoot with only the information provided. I would recommend you the followowing: If a customer is having problems with 51xx, please collect the typical information and contact Tier 2 in your region: 1) description of problem and what is known so far 2) configuration file exported from AP 3) level 7 syslog captured during problem 4) wired and wireless traces captured during the problem Quoting ECRT: "There are over 2000 messages possible messages and most indicate very specific and detailed information about AP internal state.  In general 51xx messages are not designed as clear trouble indicators for customers.  The majority of them are errors detected deep inside the AP that don't often point directly to a configuration problem on AP or MUs.  To a large degree, making sense of syslogs requires familiarity with internal AP architecture and how the various components work together. Since there are so many messages, and because they can change from version to version, it can be necessary to reference the code to get the subtler meanings.  The point is that troubleshooting with syslogs (on any product) is much more involved than simply looking up messages in a list.  If your customer has a problem, collect the info and contact Tier 2 immediately.  Remember that syslogs are most helpful when used along with other supporting info, such as the things listed above (config, traces, description of test procedure and results)." From the message you post, we can tell you only the following: ixp0 and ixp1 are the two Ethernet devices (ixp0 is LAN, ixp1 is WAN).  Not knowing how the AP was configured, how is it integrated in the network, which traffic is passing in the switch when you get this message, steps to reproduce the issue, makes it impossible to troubleshoot further.