If that’s the CMS login page, it has been heavily modified, I can only assume the CMS itself after login page was modified as well?
Looking at your page I can’t even tell if you’re using Xibo which could be ok, but I can’t even tell if you’re using software under AGPLv3 licence which is not ok, not sure what the ‘Subscribe’ button does on the ‘CMS’ login page, but that looks a bit odd to me as well.
Is Xibo source code or offer of the source code as well as AGPLv3 licence distributed to your clients by other means?
As clearly it was removed from the login page, and at least in the terms on that page I don’t see a single mention of it.
I don’t think I’ve seen this error before either, however if the CMS source code was modified, then that could explain it.
It could also be a problem with your server / php configuration (soap).
Is it 1.8.2 CMS and player?