This may be due to a permission issue.
When Umango runs in the GUI, it uses the current user's permissions. When Umango runs in the service (in the background), it is allowing the Umango job to be handled by the Umango Windows Service.
This Windows service (background) program, by default, runs as the user 'LOCAL SYSTEM', while the Umango (GUI) application runs as the currently logged in user. Because of this, your logged in user may have access permissions to the source/destination folder, while the SYSTEM user may not have access. This is a common issue when the source/destination is a network drive, where their logged in account has permissions to the source/destination folder, while the SYSTEM user is limited to permissions on local folders.
To fix this, change the Umango service logon account details:
Link to this article http://umango.com/KB?article=37