Sub-assembly needs a rebuild everytime it is opened!

This one has me stumped!
Is there an easy way of finding out what part or sub-assembly is causing
this?
The parts and sub-assemblies have been made by someone else and apart from
going though each and everyone of them, I was hoping for a quicker solution.
There are, "inserted mirrored parts", but not mirrored sub-assemblies, I
have open referenced parts selected, but I can't seem to find which one is
causing the problem.I have narrowed it down to one sub-assemble, but there
are around 300 parts/assemblies in it, this sub-assembly on its own opens up
fine!
Pete

 

Pete,

Sounds like time to dig into "Trees of Blood".

 

bob z. is not sure if what he is about to describe is the cause of your
problem, but you never know!

bob z. has seen this personally when someone created a mirrored part by
creating a 'dummy' assembly - insert the part to be mirrored in a new
assy, mirror the part, save the part and then delete the assy.

One other possibility is a circular reference in one sketch
somewhere...

This incessant rebuilding is no fun at all!

bob z.
p.s. today is bob z's five-year anniversary at his current place of
employment.

 

Thanks guys, I found that a tool box part had no constraints at all, after
adding some constraints, it now builds perfectly!
This nut was "attatched" to an assembly that has an advanced motion mate.
Ahh!
I can only think that when opening the assembly, the nut was moving.
I may be wrong, but adding the constraints has cured the problem.
Thanks again for your help