Hi,
I don't know where did you get those files, but this what I did:
Registered myself here:
http://www.nessus.org/plugins/index.php?view=register
In mail recieved as a response clicked:
http://plugins.nessus.org/manual-register.php
which let's you download all plugins (file all-2.0.tar.gz). That unfortunately can't be uploaded into CAM as is because it's larger than max. upload limit. You have to extract it, split into parts smaller than 10MB and compress again to plugins.tar.gz (7zip can be used for this)
After that, you can upload/import 2 files produced into CAM and it should work ... it worked for me ;)