[xwiki-users] Row was updated or deleted by another transaction

Erm.. what does this supposed to mean? --- on save I got this (page has no objects other than rights): com.xpn.xwiki.XWikiException: Error number 3201 in 3: Exception while saving document StageGate.WebHome Wrapped Exception: Error number 13012 in 3: Exception while saving links Wrapped Exception: Row was updated or deleted by another transaction (or unsaved-value mapping was incorrect): [com.xpn.xwiki.objects.LargeStringProperty# XWiki.Admin, --- and now getting: Error number 4001 in 4: Error while parsing velocity page BookIn.WebHome Wrapped Exception: Failed to evaluate content with id WebHome ---