Retrieving packages fails for unattended robots.Package folder is changed to a network shared location.The error would be similar to the following one. Access to the path \\filesv\users\robotaccount\Packages\test\1.0.1\ is denied.
A workaround is to turn off the Secure XAML.
It can be done by editing the UiPath.config as shown below.
1. Open UiPath.config file in the robot installation folder.
2. Change the following value to true
<add key="disableSecureXaml" value="true" />
3. Restart the UiPath Robot service.