This post follows on from my post last year about registering Service Endpoints in CRM to send messages to an Azure Service Bus.
If you make use of this functionality and were not aware of the pending certificate expiry for CRM you may have had the unpleasant experience of the messages being sent to the service bus queue (or topic etc) failing in the last week or so (as of 7 March 2015). Basically, for security enhancements the existing certificate expired and a new one was issued to authenticate against the Azure service.
All the information you need is here: http://support.microsoft.com/en-us/kb/2836034
To summarise (and in case that link no longer works): If I was organised and got this post out early, the recommendation would be to login to the access control page for your service bus namespace (https://<servicenamespace>-sb.accesscontrol.windows.net/v2/mgmt/web) and under Service Settings –> Service Identities add the new certificate for your region (this can be downloaded from your CRM instance under Settings –> Customizations –> Developer Resources or from the links in the article link above). By having the two certificates installed side by side, you would have been able to have continuous service as they transitioned over and could then remove the old certificate at your own time. Now that it is past the expiry date, if you do not have the new certificate installed you should get this installed ASAP and can just replace the existing one. Once the new certificate is installed (give or take a few minutes for the change to propagate), you should be all good to go again.
So there we go. As with a lot of certificate expiry related issues, there is little to no notification that they are about to expire, so is something that as system administrators we need to be aware of and manage accordingly. We now have a few years to get ready for the new certificate here to expire and need changing again.