It is caused by a few abilities using the same target selection method.
The problem is it tries to find a good spot to deal aoe damage based on the average center of nearby enemies.
This works in most cases but causes problems if all enemies nearby are equidistant to one center point, like here with 2 doors.
We are going to change this algorithm to use a median, so that it always picks a valid enemy location and not an average location which might be in the middle of but not even near to enemies.

OK that might be the culprit, the Unity version we use is known to crash randomly due to a false handling of USB audio devices.
When you are playing the game with your USB audio device,
can you make two things sure:
1) The USB device is setup as system default audio device: http://www.plantronics.com/asia/support/kb/detail.jsp?vfurl=/articles/en_US/How_To/Computer-Headsets-How-to-Set-the-Headset-as-the-Default-Audio-Device&c=All&lang=en_US®ion=asia
2) The USB device is set as stereo device: under Control Panel -> Sound -> "Your USB audio device" -> Configure

As far as we know this fixes the problem with Unity so the device can be used without a good chance of crashing.
So I hope you wont suffer such crashes in future.
Please let us know if it helped or not.

See for walkabilities, this is a correct prison: http://imgur.com/eW1xhL0
And this is the prison on imported Stonegate: http://imgur.com/97hOJwd

Nano Boucher please reimport the map "Stonegate" now after the large L-shape room freeze is fixed,
because prison walkabilities are wrong (units can pass and are barely blocked by the fence) and torture chamber props are rotated oddly.
Thank you

Do you by any chance use an USB audio device to hear the games sound? (when it crashed)

Here is also a list of common problems which users encounter:
http://steamcommunity.com/app/230190/discussions/0/523890681426547342/

However if you don't find your fix, please upload a log like Nutter said.
It might allow us to see what was going wrong at your end.
Cheers

Hrm... what I guess then there is still a lag issue which can break worker tasking.
You might only encounter it, when a map is literally too big and bloated with stuff for your pc.
So while this map lagged quite heavily for me, my rig was maybe still strong enough to not run into that issue.
However if you encounter this issue again, without having utter lags, please let us know.
Thanks for provided info so far and reporting anyway.