Installing SSL certificate: getting key error

Private key error (invalid format)

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I'm trying to install and SSL certificate but at the final hurdle I'm running into some problems:

I've ran the CSR, created the private key and passphrase.
Sent it to the SSL people (Geotrust) and got the CRT file back.

I've added the CRT file to the server and referenced it correctly in the vhosts file but...

then I can't restart apache!

The server has plesk installed and the Plesk interface shows this error:
Unable to set the private key: Probably, the private key format is invalid.

How can the key be the wrong format? I generated it from the same server a week ago!

[edited by: jatar_k at 1:19 pm (utc) on Mar. 16, 2007]
[edit reason] no urls thanks [/edit]

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oh well!