In the context of cloud computing and security, what could be a likely cause for an error message stating "unable to get security credentials from EC2 instance metadata service"?
A) Network connectivity issues between the EC2 instance and the external service.
B) Misconfiguration of the security group rules associated with the EC2 instance.
C) The EC2 instance metadata service is disabled or not reachable.
D) Incorrect IAM role permissions assigned to the EC2 instance.