Not sure the cause, but this change stops the error-machine:

Jan 23 15:03:43 cvs sbbs: web  0120 Request: GET /?page=001-forum.ssjs+AND+1+%3D+1&sub=mystic+AND+1+%3D+1&thread=4809+AND+1+%3D+1 HTTP/1.1
Jan 23 15:03:43 cvs sbbs: web  0120 HTTP Logon (user #0)
Jan 23 15:03:43 cvs sbbs: web  0120 Internal Redirect to: GET /index.xjs HTTP/1.1
Jan 23 15:03:43 cvs sbbs: web  0120 Handling Internal Redirect to: GET /index.xjs HTTP/1.1
Jan 23 15:03:43 cvs sbbs: web  0120 Adding query value page=001-forum.ssjs AND 1 = 1 at pos 0
Jan 23 15:03:43 cvs sbbs: web  0120 Adding query value sub=mystic AND 1 = 1 at pos 0
Jan 23 15:03:43 cvs sbbs: web  0120 Adding query value thread=4809 AND 1 = 1 at pos 0
Jan 23 15:03:43 cvs sbbs: web  0120 JavaScript: Compiling script: /sbbs/exec/xjs_handler.js
Jan 23 15:03:43 cvs sbbs: web  0120 JavaScript: Executing script: /sbbs/exec/xjs_handler.js
Jan 23 15:03:43 cvs sbbs: web  0120 HTTP Logon (user #4)
Jan 23 15:03:43 cvs sbbs: web  0120 !JavaScript  /share/sbbs/webv4/lib/pages.js line 42: TypeError: _file is undefined, Request: /index.xjs