Index: channels/chan_sip.c
===================================================================
--- channels/chan_sip.c	(revision 107825)
+++ channels/chan_sip.c	(working copy)
@@ -2165,7 +2165,21 @@
 				if (sipdebug && option_debug > 3)
 					ast_log(LOG_DEBUG, "** SIP TIMER: Cancelling retransmit of packet (reply received) Retransid #%d\n", cur->retransid);
 			}
-			AST_SCHED_DEL(sched, cur->retransid);
+			/* This odd section is designed to thwart a 
+			 * race condition in the packet scheduler. The
+			 * only way ast_sched_del will fail is if the packet
+			 * is not in the scheduler queue. The only reason
+			 * it would not be there is if the packet is currently
+			 * being re-transmitted. If that is the case, and we
+			 * have reached this point, then that means that retrans_pkt
+			 * is attempting to lock p right now. So we need to
+			 * relinquish the lock for now.
+			 */
+			while (ast_sched_del(sched, cur->retransid)) {
+				ast_mutex_unlock(&p->lock);
+				usleep(1);
+				ast_mutex_lock(&p->lock);
+			}
 			free(cur);
 			break;
 		}