If the Organization already exists, you'll need to have the proper ID for it so Ariba can match it. If it does not exist, you'll have to fill out the required fields.
It sounds like your organization already exists, so my guess is that you don't have the right ID for the organization. (And if you do have the ID, I don't think you'll need to fill out any of the other fields.)
If you can't figure it out, try posting that row here so we can help debug.
Thanks for your feedback. There were some permission right issues.