Object assignments changed in the project or network

What causes this issue?

The system displays this error in one of the following situations:
You try to save a draft to an operative project or network in which
another user has changed object assignments
Using the shared mode, you try to save a project or a network in which
another user has changed object assignments
<ZH>Note </>
The shared mode is only available if you have deactivated the default
Business Add-In (BAdI) implementation <NP>BADI_IMPL_PS_SHARED_MODE</>.
For more information, see Customizing for <LS>Project System</> under
<LS>Handling Large Projects </>-> <LS>Business Add-Ins </>-> <LS>Make
Settings for Project Editor</>.

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

System Response

The system does not allow you to save changes, and displays a message
that object assignments have been changed in the project or network.

How to fix this error?

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.