A customer cannot work with Outlook Web Access, the rrror '503 Service Unavailable' appears when trying to open OWA.
The DefaultAppPool IIS application pool on Exchange Front-end server goes down with DCOM error:
The application-specific permission settings do not grant Local Activation permission for the COM Server application with CLSID A9E69610-B80D-11D0-B9B9-00A0C922E750 to the user NT AUTHORITY\NETWORK SERVICE SID (S-1-5-20).
The Authenticated Users group is not granted with Local Activation permission for IIS Admin Service.
Check and restore activation permissions manually.
On Exchange Front-end open Start > Programs > Administrative Tools > Component Services.
Go to Console Root > Component Services > Computers > My Computer > DCOM Config > right click IIS Admin Service > Properties > Security tab > press 'Edit' button in 'Launch and Activation Permissions' field.
Make sure that Authenticated Users group account is present and granted with 'Local Activation' and 'Remote Activation' permissions. Correct it if needed.