Did you check the credentials you are using and permissions?  That is what the error indicates.

I changed my account and password, but even if I use the administrator, it won't work

Hello
Check the firewall rules and UAC https://www.veeam.com/kb4185

This indicates that the firewall is not allowing the ports through like @Stabz told

Hi @fjl - are you using the User format with: domain\user or LOCALHOST\user? I'd also try disabling windows firewall at least just to test, as was suggested. 

Since this is not expressly an “Access is Denied” issue, and to rule out the credential concerns. Could you please test using the following command “runas /u:enteryourdomain\yourdomainaccount notepad.exe. If it works, kindly check the associated permissions. There are numerous ways you can test this tho.