Cause 17 - User busy

Since upgrading to 1.2 I’m seeing the following iin my /var/log/asterisk/messages:

Nov 29 11:50:20 NOTICE[13094] app_dial.c: Unable to create channel of type ‘Zap’ (cause 17 - User busy)

Nov 29 12:02:06 WARNING[12977] chan_iax2.c: chan_iax2: ast_sched_runq ran 249 scheduled tasks all at once

These may be the cause of my “random” disconnects of IAX calls. Can anyone provide a clue?