Hello! Our help will be more effective, if you copy and send us info about your browser and the Savefrom.Net extension:
http://en.savefrom.net/user.php?info=1
We'd also need some links you can't download (to test them).
For the better understanding it'll be great to see a screenshot with the error.
We are waiting for your reply, and thank you for contacting us Savefrom.net Team!

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

Hello, before downloading a video, hold down the <Alt> button and then the download button.

Hello, before downloading a video, hold down the <Alt> button and then the download button.

Hello, please give us more details.

Hola, por favor envíenos más detalles sobre el problema.

Hello. There is no donation needed — your "Thank you" is quite enough.

Hello, before downloading a video, hold down the <Alt> button and then the download button.

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

For the better understanding it'll be great to see a screenshot with the error.