Unable to login to WEBIF

[Black Cat]

Major problem, I'm unable to login and get a server error.
Worse still is that previously I could log into WEBIF, however all I get now is:

Webif is switched off. You can switch it on from Z-Way UI or box shell

I can't get into the UI, how can I access the box shell?

[PoltoS]

You can enable it via shell. Here is the command: viewtopic.php?f=3422&t=22911&start=20#p61622