MapleSim 2015 uses the Modelica® Standard Library 3.2.1. This library is not compatible with previous versions of MapleSim. Therefore, models created in MapleSim 2015 cannot be opened in an earlier version of MapleSim.
When you first save a model created with a previous version of MapleSim in MapleSim 2015, the Model Update dialog box appears. This dialog box asks whether or not you want to create a backup copy of the original file.
Click Yes to create a backup copy of the original file. The backup copy will be compatible with your previous version of MapleSim.
After the backup is created, MapleSim 2015 automatically replaces the older components in the model with their equivalent components from the more recent Modelica Standard Library. The new model can be opened in MapleSim 2015 (or later), but it will not be compatible with previous versions of MapleSim.
For details on how to update and backup older models in MapleSim 2015, see Updating Models Created in a Previous Release of MapleSim.