Cannot run task from ECR image

I'm trying to run a task with an image from an ECR container in the same account.

When I try to run the task, it fails, with the following message:

"ResourceInitializationError: unable to pull secrets or registry auth: execution resource retrieval failed: unable to retrieve ecr registry auth: service call has been retried 1 time(s): AccessDeniedException: User: arn:aws:sts::XXXXXXXXX:assumed-rol..."

I've tried following this help page: https://aws.amazon.com/premiumsupport/knowledge-center/ecs-unable-to-pull-secrets/ But most of the situations don't apply to me.

Also, you will see that the error message is truncated. Do you know how to get the full error message?