SSH to Amazon EC2 instance using Putty in windows

I am a newbie to Amazon web services, was trying launch an Amazon instance and ssh to it using putty from windows. These are the steps I followed,

1. Created a key pair.

2. Created security group with rule for SSH and HTTP.

3. Launched and instance of EC2 using the above key pair and security group.

4. Using puttygen converted the *.pem file to *.ppk

5. Using putty tried connecting to the public dns of the instance and provided the *.ppk file.

I logged in using 'root' and 'ec2-user', and created the ppk file using SSH1 and SSH2, for all these attempts I get the following error in putty,

"Server refused our key"

Can you guys please help, any suggestions would be greatly appreciated.