Symptoms

When executing and asynchronous IPC Event to start multiple processes only one of the process was starting while the rest (as indicated by the viewflow) whent into a "Sub-process unavailable" state.
 

Diagnoses

No errors were logged by K2 on this as no error has actually occurred. In fact this is behavior is by design. Whenever an IPC Event calling multiple instances is triggered each of those child processes needs a slot. If there is not a succeeding rule to insure that parent workflow doesn't move on to the next activity until all slots have been assigned it will behave as though only one slot was assigned and therefore only start one instance before moving on to the next activity at which point no more slots will be getting made.
 

Resolution

A succeeding rule ought to be created such that all slots are assigned before the process moves to the next activity. That rule should look like:

All of oActivityInstanceDestStatus] = Completed

For further reading please see the following link:

http://help.k2.com/onlinehelp/K2blackpearl/UserGuide/current/webframe.html_IPC_Concepts.html