CO Plan Transfer is canceled because table FMBUCOPI is already active.

What causes this issue?

You have not set the option to use the table FMBUCOPI as intermediate
table even though you have already posted data in this table for
Controlling Area &V1&, Financial Management Area &V2&, fiscal year &V3&
and version &V4&

System Response

The CO plan data transfer is canceled

How to fix this error?

Verify which scenario you are working on.
If you want to work without the intermediate table FMBUCOPI, you must
delete first its records using the transaction code FMKUDELDATA. You
will have to set the original application equal to 'LOAD-CO'. This
transaction will delete the budget entry document created previously by
FMCYCOPI_CO and will delete the corresponding records in table FMBUCOPI.

Procedure for System Administrators

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.