What exactly is the error or Inventor message that you are getting.
Do all the sub assemblies reside in the current Work Directory?
I am not getting an error message but if i accept the update, it gives me a not responding situation (screen goes kinda white and I get the blue swirl) and eventually i have to close inventor out. i have let it stand 1.5 hours hoping it would update, but it does not. All i did was change one thing and it was very small change at that. I think it may have something to do with the welds that are in the IAM file. Anytime i try to do anything that changes are manipulates the welds i get this situation. I can open and decline the update and everything seems to be fine.
I hav e about 8 idw files refrencing this assembly i do not know if that matters. IAM has 30 parts and 12 weld not a complicated one at all.
Check to make sure you are current on all SP's and hot-fixes for your product.
I would start checking each file for issues (process of elimination) for a corrupt file.
You have exited from the weld module when you are trying to save the assembly