i create some models using caesar 5.10 and send to client who have version 5.00.6 build 061102.

they can not open my model

message is : Incopatibile CAESAR II file.

KemalK,
CAESAR II is not downward compatible. It means that your input files from 5.1 can not be read by any previous caesar version.its only upward compatible.

why coade is doing this i'm not sure. but it really makes life difficult for some of us

It's not something we do on purpose. New versions address new Codes, and contain new data that earlier versions won't recognize. Attempting to go back in version would mean we have to dump any unrecognized "new" data. No matter how we did this, or how many "warnings" we displayed, many users wouldn't read them - and then blame the software when the job goes downhill. (If this is news to you, you didn't read the "Distribution Letter" (at the front of the User's Guide), and I just proved my point.)

Software constantly changes - Codes are updated, new capabilities are added, new Operating Systems and technologies are addressed, and problems are resolved. You really want to be using the current Version. (The only exception to this rule is when finishing a project under the Version it started with. But in this case the Version to be used is defined in the Project Documents and the issue of "downward compatibility" is avoided.)