Not able to start docker container using Amazon ECS

Whenever I try to start a task using amazon ecs, I get the following error:

{
    "failures": [
        {
            "reason": "RESOURCE:CPU",
            "arn": "arn:aws:ecs:us-west-2:945649174862:container-instance/7380363f-488f-4a38-9774-1e1d2641fb37"
        }
    ],
    "tasks": []
}

It says CPU is not available. I have 2 images in my task definition. My AWS instance (t2 medium) has 2 cores and I allocated 700 CPU Units for each image. So, I allocated only 1400 CPU units out of 2048 available CPU units. Still ECS throws the above mentioned error whenever I try to run the task.

If I run docker commands myself with the above mentioned config, the containers are started successfully. Help me regarding how to resolve this.