Resources already exist in the plan version (see long text)

What causes this issue?

You selected the option "Reset and overwrite" when copying actual
values from fiscal year &V1& to plan version &V3& of fiscal year &V2&.
The system therefore resets and overwrites all those values in the plan
version that do not occur in the actual version. It also means that
those planning values that already existed are reset for the resources.

System Response

To prevent unwanted loss of data for resources, the system terminates
processing in the update run.

How to fix this error?

You can change the settings for this message in Customizing by
choosing: Controlling -> General Controlling ->
<DS:SIMG.SIMG_CFMENUORK3OBA5>Change Message Control</>. Enter the
following settings:
Enter "GP" as the application area.
For message 857, enter the desired message type for online processing.
To do this, use the following code:
Message type,,ID
Error message,,E
Note in window,,I
Warning,,W
No message,,-

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

Error message extract from SAP system. Copyright SAP SE.