I've found the problem in register.asp:
Locate the following on line 563-567:
if strQuote = "1" then
strSql = strSql & ", '" & ChkString(Request.Form("Quote"),"message") & "'"
else
strSql = strSql & ", ''"
end if
Add this directly after:
if strAUAnon = "1" then
strSql = strSql & ", '" & ChkString(Request.Form("AUHide"),"") & "'"
else
strSql = strSql & ", '1'"
end if