Elastix SIP channel becomes local channel?

Hi folks,
I am currently using one Elastix server which handle hundreds of SIP client and a T1 trunk. Unfortunately one of the extensions number 286 suddenly automatically forwarded to busy mailbox once the call dial to 286. From the log in the web interface, I notify that the destination channel becomes Local/75@from-internal-00000001;1 instead of normally SIP/xxx. Is there any misconfiguration there? Thanks very much for your kindly help and please do tell me if you need any info.

Asterisk uses a modified version of FreePBX that we don’t support. They have their own support community at elastix.org