When your creating your subassembly in Subassembly Composer you may want to convey to the user when something went wrong. For instance if the math doesn’t work when modeling your retaining wall and the given design height is less than the modeled dimension height. To send a message utilize the Report Message found under Miscellaneous on the Tool Box.
Fill in the Message for the error. Next provide the level of the warning. There is Error where what went wrong was disastrous, Warning where something went wrong but was recoverable, and finally Informational where you are just annoying the user with the event viewer.