Blender 2.78c, latest version from downloads page, Windows 8.1, this test has been repeated on several systems with varying hardware but the same blender versions and operating system
Blender 2.78c suffers problems, earlier versions (tested 2.65a and 2.77a) don't but those older don't support all rig features included in this file (bendy bones)
Short description of error and steps to reproduce it
Upon attempting to append the attached file (all objects selected) into another blender file (one already containing objects or a blank one), using the default options for appending but with "active layer" unticked, blender crashes. Using the command prompt lets me find errors including:
ID user decrement error: ACPoseLib (from 'D:\Users\[username]\Downloads\[folder2]\[folder1]\fileSmall.blend'): 0 <= 0
ID user decrement error: MEshape.IK.Pole.Arm.L (from 'D:\Users\[username]\Downloads\[folder2]\[folder1]\fileSmall.blend'): 0 <= 0
ID user decrement error: MECube.002 (from 'D:\Users\[username]\[folder]\[folder]\[folder]\[filename].blend'): 0 <= 0
If the pose library is deleted from the object Pilot_Metarig then the ACPoseLib error doesn't occur, but the others still occur.
Attempting to append any single object alone, or certain groups of objects at once, does not cause such a crash.
Attempts were made to get full error logs using, in command line, blender.exe --debug-all but too much text in the command line was generated so could not be copied to post here.
File which causes the bug is attached, please do not share, I hope to delete this file from here once the bug has been diagnosed