error :verify error:num=20:unable to get local issuer certificate

I am trying to develop app for Push notification, with the reference of Ray Wenderlich tutorial http://ift.tt/1bwFxJF

I have created PEM files in a local directory, then I got to the step to test whether the certificate works, and I invoked the following command from this local directory

openssl s_client -connect gateway.sandbox.push.apple.com:2195 -cert APNDemo.pem -key APNDemoKey.pem

This produced output

CONNECTED(00000003)
depth=1 /C=US/O=Entrust, Inc./OU=www.entrust.net/rpa is incorporated by reference/OU=(c) 2009 Entrust, Inc./CN=Entrust Certification Authority - L1C
verify error:num=20:unable to get local issuer certificate
verify return:0
1485:error:14094410:SSL routines:SSL3_READ_BYTES:sslv3 alert handshake failure:/SourceCache/OpenSSL098/OpenSSL098-52/src/ssl/s3_pkt.c:1125:SSL alert number 40
1485:error:140790E5:SSL routines:SSL23_WRITE:ssl handshake failure:/SourceCache/OpenSSL098/OpenSSL098-52/src/ssl/s23_lib.c:182:

Can you please help me out in finding out where I am going wrong. I have also tried out recreation of certificates but with same result.