Supplied private key data is invalid

Hey all,

I just created a new certificate (4096 SHA2) for a siteworx account and want to install the private key. But I get the following error:

» There was a problem validating the form. Please see details below.
» Supplied private key data is invalid!

Any ideas why that would happen? I've tried copy-pasting the key in several ways, no luck...

Cheers,

Michael