I'm was having a similar problem as Langar and I'm still working off my local (haven't put it on my web site yet). I got the error Langar reported when I attempted to create a new Forum. What I noted was the error occured when I attempted to create a new Forum under the last Category created. If I created another Category, then I could create a new forum under the first Category okay. Here's what I found in the code:
Forum_Details.asp - line 158 as received in the zip file downloaded today from Web Wiz:
<option value=""<% If intCatID = 0 Then Response.Write(" selected") %>>-- Select Forum Category --</option><%
Line 158 after I corrected the problem:
<option value="<% If intCatID = 0 Then Response.Write(" selected") %>">-- Select Forum Category --</option><%
Notice the double quotes after value=. The second quote should be at the other end of the script, enclosing the returned value.