IBM announced that the Apple Push Notification Service (APNS) certificate within the Sametime 8.5.x/9.0.x Proxy installation will get expired on june, 19th 2014

Updated security certificate for Push Notifications (iOS)

So please make a update NOW !!!

If you do not update the certificate (or forgot) your Sametime Proxy webchat client will not work anymore. You should get error messages inside the
proxy log (systemout.log) like this.

APNSService   W   com.ibm.collaboration.realtime.stproxy.services.APNS.APNSService.isPushAvaialble() – Connection to APNS Failed. Returning false. Exception thrown
                                 java.net.SocketException: Connection reset
    at java.net.SocketInputStream.read(SocketInputStream.java:179)
    at com.ibm.jsse2.b.a(b.java:146)
    at com.ibm.jsse2.b.b(b.java:174)
    at com.ibm.jsse2.b.a(b.java:38)
    at com.ibm.jsse2.SSLSocketImpl.a(SSLSocketImpl.java:209)
    at com.ibm.jsse2.SSLSocketImpl.h(SSLSocketImpl.java:643)
    at com.ibm.jsse2.SSLSocketImpl.a(SSLSocketImpl.java:106)
    at com.ibm.jsse2.SSLSocketImpl.startHandshake(SSLSocketImpl.java:304)
    at com.ibm.collaboration.realtime.stproxy.services.APNS.APNSService.getSSLConnection(APNSService.java:429)
    at com.ibm.collaboration.realtime.stproxy.services.APNS.APNSService.testConnection(APNSService.java:507)
    at com.ibm.collaboration.realtime.stproxy.services.push.PushService$1$1.run(PushService.java:84)

Another problem coudl be that you can´t change the Samtime Proxy configuration inside the Sametime System console, after saving you get an error

AIDSC1608E: Unable to reach the Sametime Proxy host name

This could be solved by updating the APNS key OR i had the same problem at a customer because the APNS Servernames

feedback.push.apple.com
gateway.push.apple.com

could not be resoved by DNS (so i added tha APNS addresses to the local hostfile).