Hello, in order to help you better I need the following information.
Please, send me the information listed here: http://en.savefrom.net/user.php?info=1
Do you download via the extension SaveFrom.net Helper or the website SaveFrom.net?
For the better understanding it'll be great to see a screenshot with the error.

Hello, please, send us more details regarding the problem.

Hello, please give us more details.

Hello, we’d like to help you, but we will need some info about your browser and the installed extension first.
Please, go here http://en.savefrom.net/user.php?info=1
Copy the details that you see and send them back to us.
Please also send us some video links that you can’t download.
Thank you for contacting Savefrom.Net support !

Hello, the version of the program?
What is your OS?
Could you please send a few links you can't download. We will check it out.

Hello, please, send us more details regarding the problem.

Hello, this site is not on the list of supported resources. The full list can be found here: http://en.savefrom.net

Ok, thanks for the info provided. We've forwarded it to developers to check and fix.

Hello, please, send us more details regarding the problem.

Send screenshots.

Hello,

https://addons.mozilla.org/firefox/addon/savefromnet-helper/