VertexDisplacementMap_v4 Error 0:641

Hi all,

When I try to replace Ops.Gl.ShaderEffects.VertexDisplacementMap_v2 with Ops.Gl.ShaderEffects.VertexDisplacementMap_v4, I get this:

## Shader error undefined
ERROR: 0:641: ‘mod18_map’ : no matching overloaded function found

Does anybody know what causes this?