SSL Certificate Is Not Installing Properly in IIS 8

You only need to create a temporary website with IIS 6.0. IIS 7.0 allows you to create multiple pending requests at a time.

IIS 7.0 actually has a bug that causes the renew function to generate a CSR with a very large key (much larger than you want). Because of this, it is recommended that you create a new pending request instead of selecting the renew option. Once installed you simply switch the SSL binding on the website and you won't have any downtime. This also allows you to generate a new key every time you renew which increases security.

The certificate provider (CA) doesn't care whether you use the new option or the renew option and you could use either option whether you are staying with the same CA or ordering from a new one.

You are following the right steps (http://support.microsoft.com/kb/316898/en-us), but the error likely means that you either have no enterprise certificate authority (CA) in the domain, or the CA is not accepting new certificate requests for some reason. It may also be that your installed CA is not allowing generation of "Computer" certificate types. This can be checked in the CA configuration.

The solution depends on whether you already have an enterprise CA set up and configured. If not then you need to create one (there is guidance on the Microsoft technet site, but it's not trivial) or else use another way of generating self-signed SSL certificates such as one of the free downloadable tools.