That error simply means that the module reading the neutral file crashed. This wasn't a problem in 5.10, maybe it's the neutral file (.cii). Can you sent the file in to "techsupport@coade.com" so we can try it here?
As to your question, the answer is "maybe". The ".cii" neutral file can contain all of the necessary data for a complete CAESAR II model. However, we have seen some neutral files, created by some software packages that are a little bit incomplete (missing loads, missing boundary conditions, etc). In these instances, you would have to really verify the CAESAR II model for completeness. However, once you've transferred a few models, you'll know what to look for.
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Regards,
Richard Ay - Consultant