After completing an Exchange Hybrid Configuration wizard on a customer, we noticed that the free-busy information wasn’t working when an on-premises user was trying to retrieve information from a migrated user to Office 365. In this Tutorial, we are going to shed some light to fix the issue.
During the troubleshooting, we noticed that all cmdlets that were requesting information from Office 365 were failing, as depicted in the image below.
We went one step further and we tried to open a website (office.com) and we got a certificate error as well.
After some time troubleshooting and comparing with a server that did not have the issue, we found out the culprit: Turn off Automatic Root Certificates Updates was enabled on the server. In order to fix it, open gpedit.msc, expand Computer Configuration, Administrative Templates, System, Internet Communication Management, Internet Communication settings, and change it to Not configured or Disabled.
No restart is required, try to access any SSL site and if you don’t have any issues, try the PowerShell cmdlets. In my customer’s case, the free-busy start working like a charm.