When you attempt to install/uninstall Mail Agents/Shared Components from a server, an "Access Denied" message pops up while the wizard is processing, but when you click "OK", the process appears to continue, then freezes.
Also, you may notice that the "Quest Agent Installer Service" is running on the server using credentials from another domain.
This may be caused by another server in the opposite domain with the same name. This may cause the Quest Agent Installer service to use the wrong domain's credentials.
In this scenario, check to see if a server with the same name exists in the opposite domain.
If such a server exists, this must be resolved by renaming one of the servers. You can also remove it from the Migration Manager SQL database (if it is not involved in the migration) by right-clicking it and selecting "Remove Server From Database".