Need help with mirroring object

Hi all,
This I’m sure is a common question, I’m currently working on a project and for some reason it won’t allow me to mirror. It did it before I updated the model but for some reason it fails to do it now with the common response on the error. Can someone please help me problem solve this issue. Ive attached a picture to give you an idea of what I’m working on. Thanks in advance


Make sure the entire body (or bodies) are selected, then do the Mirror.
If you try to mirror a face it won’t work in this case.