Autoupgrade from shared directory not working on Windows

For windows, the Autoupgrade has certain prerequisites:

1. The Host Agent system must have access to the share. The SAPHostExec service is doing the autoupgrade and this service is running as Local System Account. ( One can read more about the Local System Account on http://msdn.microsoft.com/en-us/library/windows/desktop/ms684190 ) Hence, the <System>$ account must have access to the shared directory.
2. Autoupgrade is working with UNC paths only. "Mounted" directories (e.g. as Drive X:) do not work.

If the Host Agent System and the System with the shared directory are located in different windows domains, there must be a one way trust to access the share. That means, the domain of system A (the system with the shared directory) has to trust the domain of system B (the system with the Host Agent).

See http://msdn.microsoft.com/en-us/library/cc237016%28v=prot.10%29.aspx for more information on how to setup a domain trust.