The NoCredentialsError in the Boto3 library occurs when AWS credentials are missing, invalid, or cannot be located, preventing a connection to AWS services. These credentials, usually stored in the ~/.aws/credentials file, consist of an access key and a secret access key, and are essential for authorization. The error is typically encountered when a Python script attempts to connect to an AWS resource, such as an S3 bucket, without proper credentials. The solution involves checking the existence and correctness of the credentials file, and possibly regenerating keys through the AWS Management Console if necessary. For persistent issues, contacting Amazon may be required. Additionally, tools like Rollbar can help manage code errors by providing real-time tracking and analysis, thus aiding in smoother deployments.