Friday, February 3, 2017

Exchange 2016 100% CPU and Event ID 5011 "MSExchangeServicesAppPool"

This post is mostly for my own reference, but just in case you come across the same issue, I'll outline the problem and the fix.

We recently migrated several hundred users from Notes to my Exchange 2016 CU2 environment and shortly after the migrations, one of my three mailbox servers was getting constantly hammered.

The CPU was at 100% usage, performance was terrible, and it even caused my Kemp load balancer to flap the virtual services on this server every 30 seconds or so. In particular the MAPI and EWS services.

That led me to start checking what was up with EWS.

The System Event log was full of the following error:

Log Name:      System
Source:        Microsoft-Windows-WAS
Date:          1/28/2017 3:11:50 PM
Event ID:      5011
Task Category: None
Level:         Warning
Keywords:      Classic
User:          N/A
Computer:      EXCH16-MBX1
A process serving application pool 'MSExchangeServicesAppPool' suffered a fatal communication error with the Windows Process Activation Service. The process id was '18076'. The data field contains the error number.

I remembered that one of our admins was testing out an EWS Retention policy script and had installed the Exchange Web Services Managed API 2.2  on this box.

So, I uninstalled the API 2.2 and bingo! Problem solved; CPU was back to normal, all client connections were now stable.

As a workaround, we installed the EWS Managed API 2.2 on our DAG witness server (since it has the Exchange tools installed on it) and now run the script from there.

It works!


  1. Solved issues we were having with Exchange 2016 as well. We were seeing issues with Out of Office not working in Outlook and Public folders being slow to load and a slew of other problems. Thanks for sharing!

  2. Having similar problems but cannot find any documentation on how to uninstall Exchange Web Services Managed API 2.2. Are you aware of anyway to tell if its installed on Exchange 2016 Server?

    1. Hi Jon,
      EWS API 2.2 is a manual install, so it should be listed in Add/Remove Programs if it's on that box.

  3. This solved issues we had as well involving Outlook for Mac being disconnected from Exchange 2016. Looks like it was installed alongside a trial of ManageEngine's Exchange Reporter Plus.

    1. Thanks for the heads-up about ManageEngine! Glad you got it sorted