In order to create a subsystem, the mother part of subsystem must be outside of subsystem and cannot be accessed within subsystem. When a user creates a joint or force, its mother part may be the ground, or the mother part of subsystem, or one of subsystem bodies. A mother body of subsystem conformed by clicking the point. To exit child subsystem mode, click Exit on right-click menu or Exit icon of the Exit group in the Professional tab.
Figure 1 Mother body of Subsystem
Figure 2 Subsystem icon of the Subgystem group in the Professional tab