Hi Colin,
I noticed an error something like this awhile back when I tried using a fresh xowiki install. I haven't tested lately, but my limited experience with most all esoteric xowiki errors are overcome by:
1. restarting naviserver after an install and before doing anything else.
2. waiting an hour (or as much as a day) before using xowiki;
Explanation of #2: There are some critical background xowiki/pg related init processes started when xowiki is installed. Also, some xotcl/xowiki processes apparently return incomplete results if process time is too long. When I install on *very* slow/limited systems, some part of the background init appears to timeout ( and fail silently), subsequently resulting in esoteric errors. This is not necessarily an xowiki specific issue. One time about 14 years ago, something similar was happening to early openacs installations on vm installed in an overloaded server.
Hope that helps.
