Database error

From LoveToKnow 1911

A database query syntax error has occurred. This may indicate a bug in the software. The last attempted database query was:

(SQL query hidden)

from within function "MediaWikiBagOStuff:_doquery". MySQL returned error "1062: Duplicate entry 'legacy_1911:pcache:idhash:0-1!1!0!1!0!1!0!!en' for key 'keyname' (db1)".