Installed Drupal Module of Mandril , it continuously gives me 500: You must specify a key value -

[Nadir]

Hi,

I am seeing the following error in the error logs

Error sending email from nor...@mywebsite.org to nhaj...@mywebsite.org. 500: You must specify a key value - Array 

I have double checked and verified that the Api key is correct not sure why it keeps showing me this error. Any one else run in to this? Also is there any other way to test if this is really the issue?

Thanks.