Vray Proxy Renders black in animation

[kellyctv]

Im having a problem with vray proxies in an animation I'm running. In this one planting bed every few frames black boxes appear instead of the vray proxy. It's only this one area of the scene. As you can see with the attached image it's in the ground cover, previously it was with the trees, Then I replaced them and the problem migrated to the groundcover. any help would be great.

Kelly