SSL error while uploading cookbooks to hosted chef

I’m trying to upload a bunch of cookbooks to hosted chef server using the following command.

knife cookbook upload -a -o /tmp/cookbooks/ -c /tmp/chef/knife.rb

knife.rb looks similar as below.
current_dir = File.dirname(FILE)
log_level :info
log_location STDOUT
node_name "username"
client_key "#{current_dir}/username.pem"
validation_client_name "validator"
validation_key "#{current_dir}/validator.pem"
chef_server_url “chefserverurl”

Few of the cookbooks are getting uploaded but it’s failing after some cookbooks with SSL validation error as described below.
DEBUG: ---- HTTP Status and Header Data: ----
DEBUG: HTTP 1.1 200 OK
DEBUG: Initiating PUT to https://s3-external-1.amazonaws.com/opscode-platform-production-data/organization-09469edacd8b383e29deb24b70e21c7c/checksum-14892bae37b8edc11b8e3dae71a3f8d1?AWSAccessKeyId=AKIAIQKPG2CTSTRVDO4Q&Expires=1457158196&Signature=yVZLkAzG57jCmlFJVggjMpXy4/4%3D
DEBUG: X-OPS-AUTHORIZATION-5: l4kSChxELOkW1N/CRPACs6AX3CpVOuucFx2tBnFQhkeEU+D0W9tnwVRkXuxN
DEBUG: date: Sat, 05 Mar 2016 05:55:11 GMT
DEBUG: content-md5: FVbuXR0ePH0l0J7dZntdZg==
DEBUG: Chef::HTTP calling Chef::HTTP::CookieManager#handle_request
DEBUG: accept: application/json
DEBUG: HTTP 1.1 200 OK
DEBUG: x-amz-id-2: UB9txRXh0eqZs+HaOTB4A/oh4KIoZesTIj2RCZSLGZ8ALulxcF5ZZbcD3bc9+h4Y
ERROR: SSL Validation failure connecting to host: s3-external-1.amazonaws.com - SSL_connect SYSCALL returned=5 errno=0 state=SSLv3 read finished A
ERROR: SSL Validation failure connecting to host: s3-external-1.amazonaws.com - SSL_connect SYSCALL returned=5 errno=0 state=SSLv3 read finished A
DEBUG: etag: "13fee0703d9c3bbb65ac1b40be674b3a"
DEBUG: ---- HTTP Request Header Data: ----

Any help would be much appreciated.

Thanks,
Prakash