Then it still runs under a user that doesn't have access to the share. Are you sure you filled in the correct credentials and restarted the service? Also, is Y: a permanent mapping?
Not sure, but does the service really get access to a user mapped network share?
I use the UNC path instead, and don't have any problem.
Services and Redirected Drives (Windows)
From above link!
Drive letters are not global to the system. Each logon session receives its own set of drive letters from A to Z. Therefore, redirected drives cannot be shared between processes running under different user accounts. Moreover, a service (or any process running within its own logon session) cannot access the drive letters that were established within a different logon session.