Solved can't connect to bnet

As always, you are supposed to give us more information such as what operating system is he using, what antivirus, is windows defender turned off, how about DEP settings?
Have you tried these solutions http://forum.europebattle.net/threads/fix-diablo-ii-common-errors.532466/ ?

 

I was assuming he was using bitdefender. (using bitdefender total security 2017 myself)
Did you read our notice about bitdefender on the connect page? Is he using free version of bitdefender or paid one aka internet security, total security, etc?

Please refer to this image to see what he needs to disable before opening the game and clicking battlenet button https://i.gyazo.com/9956b593d092ce022a7eb34115e785b1.png
Note: this option is available in the paid version of bitdefender, the free version may not give you the possibility to disable false-positive errors which is known for causing issues with many other applications.

If you still can't figure it out send me a private message with his skype id and I'll be online in about ~30 minutes to assist him remotely.

It's been fixed, the end user forgot to disable bitdefender's `active thread control`, thus it was blocking the connection.