HDLC Abort

Dear All,

I am setting up freepbx with the E1 and getting the following error message:-

NOTICE[3140] chan_dahdi.c: PRI got event: HDLC Abort (6) on Primary D-channel of span 1

Please let me know the cause of the same and also some time the call is being disconnected abnormally and sometimes it is not audible.

Pls help.