The personal isogen verion for CAESAR II 5.10 is 5.6.9.5, and the for 5.20 is 6.3.0.0. That may be the reason, but I am not sure. Try the suggestion I posted previously, that will work. You can send me the 5.10 file, I can take a look.
Regards,
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Shawn Zhong
CADWorx & Analysis Solutions
Intergraph Process, Power, & Marine