/ Error: file: D:/Autodesk/Maya2019/scripts/others/doMirrorSkinWeightsArgList.mel line 84: saco is not in a skinCluster.

That's the error I get when attempting to mirror my mesh (yeah, not the joints). I try with another one and the error doesn't come up so I guess is something related to that bind-skinned mesh and not the general settings. Good to mention that it's not the first time I mirror this mesh but I've done some little changes here and there in my rig file (and closed it and opened several times) so I don't know what's pasando.

Any help would be highly appreciated,