Both files open OK independantly, but when I try to insert the sub-assembly, SW crashes.
It's going to be very difficult for us to help without the files, or more information. I assume this only happens with these particular files? This may be a problem to take to your VAR.
I have a fairly complex multi-level assembly. I can open the top level assembly OK, but when I try to open the mid level assembly the program crashes. If I edit the assembly from in the top level, and suppress all the sub-assemblies inside it I can then open it. After unsuppressing components one at a time I discovered which sub assembly was causing it to crash. however I can open that lower level assembly independently and there are no apparent issues. I tried deleting the sub assembly from the mid level and re-inserting it to maybe change IDs but that didn't work either.
I would suspect;
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