I have BE 2015 on the server and 8 other computers connected to it. We had set up the backup of all computers and it was working for the first year. After one year, Symantec BE stopped backing up of the other comouters and it says you need a license key for the windows agents.
This license costs around £350, but I am not sure how many do I need. Do I need one license for all computers or one for each?
One Remote Agent license per remote server.
BE 15 Licensing Guide - http://static.symanteccloud.com/estore/resources/en/be-2015-licensing-guide.pdf
...if you have an application like SQL or Exchange, then you need a database agent license, and this license includes the ability to install the Remote Agent. with an agent license you wouldn't require a RAWS license.
If these are all file and print, then 1 RAWS per server.