Nuspec file renaming is not working

I have a project groups and added a nuspec file in the project. In teamcity project configuration also passing the /p:OctopusNuSpecFileName=Groups.IUS.nuspec to msbuild. But still it is not changing the name of that package to the one I am passing in build parameter. I want groups package to be renamed as groups.IUS. Artefact that it creates is still Groups.
Any Idea what I am doing wrong
Please find screen shots of my settings.



Thanks, the parameter to pass was changed in OctoPack 2.0 - you now need to use OctoPack as the prefix:



Saved my day. thank you very much. Now working fine.