You have a number of issues with this installation, Michele which I highly recommend addressing.
* Your themes are out of date, indicating that an update(s) was performed incompletely. Your control panel is using the old theme, and not even an up to date version of it, so there are many display errors, as well as missing images.
* You are running a live site in Debug mode 2 (errors displayed to everyone). This is highly insecure for a public site.
* The error you reported happening when logging out is not what you are actually getting, which is why I was dumbfounded as to how you could be seeing that error when logging out. The query error for the actual error you are getting is:
Query: SELECT pref_forum_url, pref_forum_name FROM exp_forum_prefs WHERE pref_id='1'
It is imperative when seeking assistance that any error messages are carefully and precisely communicated in order for us to be able to assist you. This error relates to the updates not having being completed properly. Your member module files are out of date, and is the source of the error. So I’m recommending that you:
1) Change your Debug setting to 1 (show errors only to logged in Super Admins)
2) Download a fresh copy of ExpressionEngine and the Forum Module. Since your database is in good shape, you do not need to perform a full upgrade, but the instructions for updating to the latest build.
3) Then go back to the upgrade instructions and at the bottom of the page, view and take action on each of the version specific instructions from the oldest version of EE that you were running up through version 1.6.2. For your themes, you may find it simplest to simply overwrite them with the current themes from the new download, and work any modifications you have made back into these known good files.
It might be a good idea to hire an experienced ExpressionEngine user to help you with this process if you are not comfortable with handling the above course of action on your own.