The most common cause of this issue is an unresponsive ClickToRunSvc service.
To resolve it, check to see if OfficeClickToRun.exe is running during the hang. If it is, stop the service by the following these steps:
Use any of these methods:
OfficeClickToRun.exe hosts the ClickToRunSvc service, which hosts a number of ALPC endpoints. One of those ALPC ports is "\RPC Control\C2RClientAPI_Server_System16". Outlook and Skype for Business attempt to connect to "\RPC Control\C2RClientAPI_Server_System16" during startup and initialization. An unresponsive ClickToRunSvc service will cause an inability to communicate with the above-mentioned ALPC port which, in turn, will cause Outlook and Skype for Business to hang.
If Outlook continues to hang, refer to the suggestions below for some more recommended troubleshooting steps:
- If Outlook continues to hang, OfficeClickToRun.exe can be uninstalled. Refer to this Microsoft article for details on how to do this.
- If you are running Outlook 2016, follow the steps in this Microsoft article to configure Outlook to always run maximized.
- Repair the Office installation, by following the steps in this article.
- Run the Office Configuration Analyzer Tool to check your Office installation. This can be downloaded from this Microsoft article.