I had following observations and now doubt if these are particular to my system or valid in general.

In a multi-user environment, if accidentally a user tries to open a model that has already been opened by another user then Caesar does not impose any restriction on the 2nd user to open the model. This mean that during input session the changes saved later will be preserved while those made earlier will be discarded, resulting in a model that may not meet the expectations of one or both the users.
However if both users try to run the model simultaneously the application of one (or may be both) crashes giving varying sort of error message. Probably this is because both applications try to copy the intermediate file with same name in the same directory.
Even if the run is successful the results will be in doubt.

Any comments?

Two users can not work on the same model! If you attempt this (accidentally or not) there is no telling what the outcome will be.

If two users need to work in the same data directory, each user should set his own ID, so that the intermediate communication files will be appended with this ID as a suffix. You can set this up via the "Miscellaneous" tab of the configuration module.