Hey,
I don't know about this particular error, though can say Wikibase is no
longer compatible with MediaWiki 1.23. Unfortunately retaining
compatibility with a stable MediaWiki version, and third party support in
general, does not appear to be high on the priority list of the Wikidata
team. So I can only recommend against third parities using the software in
serious contexts for now.
Cheers
--
Jeroen De Dauw -
http://www.bn2vs.com
Software craftsmanship advocate
Evil software architect at Wikimedia Germany
~=[,,_,,]:3