Activity input &/& cannot be planned manually for cost center &

What causes this issue?

The activity input of &v1&/&v2& on cost center &V3& has already been
determined using dependency. Any change due to data transfer cannot
be made.

System Response

The planned record to be transferred is written to the error log.

How to fix this error?

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.