Agile ACS Destination to alternate network server

We are attempting to setup an ACS File destination (e.g. \\server2\agile\pdx) to an alternate server share within our network but continue to receive the message: "The required path does not exist or the user does not have write privilege" when clicking the "Test Destination" button. When using a directory on the local machine (e.g. d:\temp or \\server1\d:\temp), the test is successful.

Read/Write access from the application server to the destination server has been granted at the machine level. Do additional grant privileges need to be provided? Is there a trick to setting the target path to an alternate server? The Agile ACS manual is a little vague when it comes to this information, although it does briefly mention the user "agileuser".