Error occured while retrieving and decrypting credentials

Dear Coder,
First of all, alot of thanks for putting this great plugin. It has removed the depedency for installing nrpe on each instance. I am able to install all depedencies. Now when i tried to run the script i am having this error. Can you please tell me what i am missing here.

Error occured while retrieving and decrypting credentials for instance i-XXXXXXXXX on Amazon Server: ec2-XXXXXXXXX-compute-1.amazonaws.com: key must be 16 bytes