Per your provided error, there’s a conflict with existing Niagara components in your project.
Is the VFX you are opening tied to a Niagara system? If so, try to disassociate from it, then re-open it. If the issue persists, remove that particular Niagara cluster (or all of Niagara if the error continues).
In case this approach fails, please check the following thread on a similar situation, and test their methods for your scenario: