When accessing the List created using BCS service for the first time the user might get Access denied error. Basically the external content type is created but not added any user for the access in the BCS service application in the central admin. So navigate to the Manage Service Application page in Central Admin. Click on the BCS Services. The external content type will be listed in the List of BCS. Click on the Content Type and Click on Set Permissions. The below screen will pop up and add the users to the list and assign permission.