c5738d67__Codes___Telecomuserguides_com__Explanation
[0] 266 [Action] Unplug the AC15A private circuit from the KSU. Consult the documentation for the correct location of the AC15A ports, and then plug the AC15A private circuit into one of the allowable ports. [Explanation] 
An AC15A private circuit is plugged into a telephone port that is not in the allowable range for AC15A private circuits.
Nortel Systems User Guides, Nortel Error Codes - Telecomuserguides.com
Explanation