I'm having the same issue, and I've tried on various browsers and machines. Keep getting "Error" Sorry an error has occurred. Does the administration of this website not care? Its been like this for weeks.
Replicating this problem is inconsistent at best for myself; however, when it does happen, the build finder still seems to work in finding the builds you're looking for---it just also produces an annoying error.
It would be REALLY NICE if we could enter spells like "Skeletal Mage" again.
If you press the "Filter" button without enrtering items or non-items, the scripts generate this URL: