Unfortunately, some Mac users have reported an issue with nugster after installing the most recent MacOS where nugster shows an error message but the files have actually downloaded successfully. 
To resolve this issue, please follow these steps:

-Install the nugster download manager using the installer application to your Applications folder, then exit the installer
-Go to System Preferences>Security & Privacy - click the Privacy Tab
-If necessary, enter your Apple Username and Password to unlock the Security and Privacy Preference
-Ensure that the nugster app has "Full Disk Access"