I\'m currently inside the 30-day free trial for Google Apps for business (billing set up, so will start non-free trial soon). I\'m attempting to set up SSL for a custom doma
For me, it was because my private.key was in the wrong format.
If your key starts with ---BEGIN PRIVATE KEY--- then you need to convert it to an RSA key.
openssl rsa -in private.key -out private_rsa.key
Then you should see ---BEGIN RSA PRIVATE KEY--- at the beginning of the private_rsa.key which you use with GAE.